UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


MODERN 
Electrical  Construction 

A  RELIABLE,  PRACTICAL  GUIDE  FOR  THE 
BEGINNER  IN  ELECTRICAL  CONSTRUCTION 
SHOWING  THE  LATEST  APPROVED  METHODS 
OF  INSTALLING  WORK  OF  ALL  KINDS  AC- 
CORDING TO  THE  SAFETY  RULES  OF  THE 

National  Board  of  Fire  Underwriters 


By 

HENRY  C.  HORSTMANN 
VICTOR  H.  TOUSLEY 

Authors  of  "Modern  Wiring  Diagrams  and  Descriptions' 


3flllu0tratrD 


CHICAGO 

FREDERICK].  DRAKE  &  CO.,  PUBLISHERS 
1905 


COPYRIGHT,  1904 
BY 

HORSTMANN  AND  TOUSLEY 


TK 


PREFACE 


In  this  volume  an  attempt  is  made  to  provide  the  beginner 

in  electrical  construction  work  with  a  reliable,  practical  guide ; 

one  that  is  to  tell  him  exactly  how  to  install  his  work  in  ac- 

.y   cordance  with  the  latest  approved  methods. 

£         It  is  also  intended  to  give  such  an  elaboration  of  "safety 

rules"  as  shall  make  the  book  valuable  to  the  finished  work- 

-    man  as  well.   To  this  end  the  rules  of  the  "National  Electrical 

g   Code"  of  the  National  Board  of  Fire  Underwriters  have  been 

U   given  in  full,  and  used  as  a  text  in  connection  with  which 

£  there  is  interspersed  in  the  proper  places  a  complete  explana- 

^f   tion  of  such  work  as  the  rules  may  apply  to.    This  method  of 

teaching  and  explaining  practical  electricity  may  at  first  glance 

seem  somewhat  haphazard,  but  it  resembles  very  closely  the 

-factual  method  by  which  the  most  successful,  practical  work- 

W  men  have  learned'  the  trade.     It  is  thought  that  explanations 

pertaining  directly  to  the  work  in  hand  will  be  more  deeply 

considered   and  more   likely  to  be   fully  comprehended  than 

explanations  necessarily  more  abstract. 

It  should  be  noted  that,  while  the  rules  published  in  the 
"National   Electrical   Code"  are  standard  and  work  done  in 


conformity  with  them  will  be  first-class,  several  of  the  larger 
cities  have  ordinances  governing  electrical  work  which  con- 
flict in  some  details  with  these  rules.  Workers  in  such  cities 
should,  therefore,  provide  themselves  with  copies  of  these 
ordinances  (usually  obtainable  without  charge),  and  compare 
them  with  the  rules  given  in  this  work.  It  is  necessary  for 
the  electrical  worker  at  all  times  to  keep  himself  posted,  for 
safety  rules  are  liable  to  change. 

The  tables  concerning  screws,  nails,  number  of  wires  that 
can  be  used  in  conduit,  etc.,  are  especially  prepared  for  this 
volume,  and  give  to  it  particular  value  for  practical  men. 

THE  AUTHORS. 


CHAPTER  I. 
The  Electric  Current. 

It  is  quite  customary  and  convenient  to  speak  of  that 
agency  by  which  electrical  phenomena,  such  as  heat,  light, 
magnetism,  and  chemical  action  are  produced  as  the  electric 
current.  In  many  ways  this  current  is  quite  analogous  to  cur- 
rents of  air  or  water.  Just  as  water  tends  to  flow  from  a 
higher  to  a  lower  level,  and  air  from  a  region  of  greater 
density  or  pressure  to  one  of  lesser  density,  so  do  currents  of 
electricity  flow  from  a  region  of  high  pressure  to  one  of  low 
pressure.  Currents  of  electricity  form  no  exception  whatever 
to  the  general  law  of  all  action,  which  is  along  the  lines  of 
least  resistance.  It  must  not  be  understood,  however,  that 
electricity  actually  flows  in  or  along  a  conductor,  as  water 
does  in  a  pipe,  and  the  analogy  must  not  be  carried  too  far,  for 
the  flow  of  water  in  pipes  is  influenced  by  many  conditions 
which  do  not  influence  a  flow  of  electricity  at  all,  and  vice 
versa ;  there  are  conditions  surrounding  conductors,  which 
influence  the  flow  of  electricity  which  do  not  affect  the  flow 
of  water. 

Above  all,  let  it  be  understood  that  electricity  is  not  inde- 
pendent energy,  any  more  than  the  belt  which  gives  motion 
to  a  pulley  is.  In  other  words,  it  is  not  a  prime  mover,  it  is 
simply  a  medium  which  may  be  used  for  the  transmission  of 
energy,  just  as  the  belt  is  used.  To  use  electricity  as  a 
medium  for  the  transmission  of  energy,  it  must  be,  we  may 
say,  compressed,  or,  to  use  a  more  properly  technical  expres- 
sion, a  difference  of  potential  or  pressure  must  be  created  in 
a  system  of  conductors.  This  is  very  similar  to  the  use  of  air 


8  MODERN   ELECTRICAL  CONSTRUCTION. 

for  power  transmission ;  this  must  also  be  compressed  so  that 
a  difference  of  pressure  exists  within  a  system  of  piping. 

It  is  the  flow  of  electricity  or  air  which  takes  place  when 
switches  or  valves  are  operated  and  which  tends  to  equalize 
this  pressure,  i.  e.,  flow  from  high  to  lo//  pressure,  that  does 
our  work.  The  real  energy,  however,  (so  far  as  we  are  con- 
cerned), to  which  we  must  look  for  our  initial  motion  in 
either  case  is  derived  from  the  coal  which  generates  steam; 
or,  in  the  case  of  water-driven  machinery,  the  rays  of  the  sun 
which  evaporate  water,  allowing  it  to  be  carried  to  higher 
levels,  from  whence  it  flows  downward  over  dams  ar.d  falls 
on  its  way  back  to  the  lowest  level.  In  the  battery,  the  real 
energy  is  that  of  chemical  action,  which  is  transformed  into 
electrical  energy. 

The  flow  of  current  can  take  place  only  in  a  system  of 
conductors  which  usually,  for  convenience,  are  made  in  the 
form  of  wires.  The  current  for  practical  purposes  may  be 
considered  as  flowing  along  such  wires  only.  It  is  not,  how- 


Figure  1 

ever,  necessary  that  these  wires  should  be  of  any  particular 
size,  or  consist  all  of  the  same  material.  In  an  electric  bat- 
tery, part  of  the  circuit  consists  of  the  liquid  contained  within 
the  battery;  the  rest  being  made  up  usually  of  wire.  In  an 
incandescent  light  circuit  part  of  the  circuit  consists  of  the 


ELECTRIC  CURRENT.  9 

lamp  filament  (usually  carbon),  while  the  balance  of  the  cir- 
cuit consists  of  copper  wire. 

The  flow  of  current  is  also  said  to  have  a  certain  direction ; 
that  is,  it  is  noticed  that  many  of  its  effects  are  reversed  when 
the  terminals  of  the  battery  are  reversed.  Referring  to  Fig. 
1,  which  shows  a  battery  of  three  cells,  the  current  flows  from 
the  copper  element  at  bottom  of  jar  1,  along  the  wire  to  the 
zinc  element  at  top  of  jar  2,  thence  through  the  liquid  to  the 
copper  element  at  bottom  of  jar  2,  and  from  there  to  the  zinc 
at  top  of  jar  3,  etc.,  and  finally  through  the  wire  a  back  to 
the  starting  point.  Within  the  battery  the  current  flows  from 
the  zinc  to  the  copper  and  the  decomposition  of  the  zinc  gen- 
erates the  current.  In  the  wire  outside  of  the  battery  the  cur- 
rent flows  from  the  copper  to  the  zinc  as  indicated  by  arrows. 
The  combination  of  battery  and  wire  is  known  as  an  electric 
circuit.  The  current  will  flow  in  this  circuit  only  while  it 
is  complete,  that  is  while  each  wire  connects  to  its  proper 
place  as  shown.  If  any  wire  is  disconnected,  the  current  flow 
v.ill  cease.  Such  a  circuit  is  said  to  be  open,  but  when  all 
connections  are  properly  made  it  is  said  to  be  closed. 

Work  can  be  obtained  from  a  flow  of  current  in  many 
ways.  If  the  current  be  forced  to  flow  over  a  wire  which  is 
very  small  in  proportion  to  the  current  carried,  it  will  be 
heated  thereby  and  finally  melted  if  the  current  is  excessive. 
This  is  how  electric  light  is  obtained. 

If  a  wire  carrying  current  be  wound  many  times  about 
an  iron  bar  this  bar  becomes  a  magnet ;  that  is,  while  the  cur- 
rent is  flowing  around  it,  the  bar  has  the  power  to  attract 
other  objects  of  iron  or  steel.  The  bar  if  made  of  well  an- 
nealed iron  will  be  a  magnet  while  current  is  flowing  around 
it,  but  will  cease  to  be  magnetic  whenever  the  current  flow 
ceases.  Upon  this  fact  the  operation  of  electric  bells,  telegraph 
instruments  and  motors  is  based. 

If  a  current  of  electricity  flow  through  a  properly  arranged 


10  MODERN  ELECTRICAL  CONSTRUCTION. 

"bath,"  one  of  the  plates  will  be  gradually  consumed  and  the 
other  increased  in  weight.  This  effect  is  made  use  of  in 
electro-plating,  etc.  If  the  jar  contains  water  slightly  acid- 
ulated and  the  current  flows  through  it,  the  water  will  be 
decomposed  and  oxygen  and  hydrogen  gas  will  be  formed. 
This  and  many  kindred  effects  are  daily  used  in  thousands  of 
chemical  laboratories. 

•  If  a  wire  carrying  an  electric  current  be  placed  very  close 
to  another  wire  forming  a  closed  circuit,  a  wave  of  current 
will  be  induced  in  that  wire  every  time  the  current  in  the 
other  is  made  or  broken,  i.  e.,  whenever  it  starts  to  flow  or 
stops  flowing.  This  fact  forms  the  basis  of  the  alternating 
current  transformer. 

All  of  these  facts  are  used  sometimes  together,  sometimes 
sir.gly  in  measuring  the  electric  current. 


Conductors  and  Insulators. 

Electrically  speaking,  all  substances  are  divided  into  two 
classes.  They  are  either  conductors  or  insulators.  By  thi* 
is  not  meant  that  some  substances  can  carry  no  current  at 
all,  for,  as  a  matter  of  fact,  there  is  no  such  thing  as  either  a 
perfect  conductor  or  a  pecfect  insulator.  A  current  of  elec- 
tricity can  be  forced  through  any  substance,  provided  the  pres- 
sure (E.  M.  F.)  be  made  great  enough,  and  there  is  no  easier 
path  open  to  the  current.  The  two  terms,  conductor  and 
insulator,  are  relative  terms  and  must  be  understood  simply 
to  mean  that  the  electrical  resistance  of  a  good  conductor  is 
infinitesimally  small  as  compared  to  that  of  a  good  insulator. 
The  lower  the  specific  resistance  of  any  substance,  the  better 
its  conducting  qualities;  the  higher  the  specific  resistance  of 
any  substance,  the  better  will  be  its  insulating  qualities. 

At  the  left  is  given  a  list  of  good  conductors,  in  the  order 
of  their  conductivity,  the  figures  representing  the  relative  con- 


ELECTRO-  MOTIVE-FORCE. 


11 


ductivity  of  these  metals.  A  list  of  insulators  is  given  at  the 
right;  all  of  these  are  more  or. less  affected  by  moisture,  los- 
ing their  insulating  qualities  when  wet. 


Silver    100.0  Dry  air. 

Copper   94.0  Rubber. 

Gold    73.0  Paraffin. 

"Platinum    16.6  Slate. 

Iron    15.5  Marble. 

Tin    11.4  Glass. 

Lead    7.6  Porcelain. 

Bismuth    ..  ,1.1  Mica. 


Fiber. 
Wood. 
Shellac. 


Pressure  or  Electro-Motive  Force. 

Currents  of  electricity  flow  only  in  obedience  to  electrical 
pressure.  This  pressure  is  measured  and  expressed  in  volts, 
the  unit  of  electrical  pressure  being  the  volt.  If  we  speak 
of  water  or  steam  pressure,  we  speak  of  it  in  pounds,  the 
pound  being  the  unit  of  measurement.  In  speaking  of  elec- 
trical pressure  we  refer  to  it  as  of  so  many  volts.  There  is  no 
direct  connection  between  the  pound  and  the  volt,  but  each 
in  its  place  means  about  the  same  thing. 

The  volt  is  defined  as  that  difference  of  potential  (pres- 
sure) that  must  be  maintained  to  force  a  current  of  one 
ampere  through  a  resistance  of  one  ohm. 

If  we  have  a  resistance  greater  than  one  ohm  and  wish  to 
send  a  current  of  one  ampere  through  it,  we  can  do  so  by 
increasing  the  pressure  or  voltage,  as  it  is  termed,  accordingly. 
The  current  flowing  in  a  circuit  can  also  be  reduced  by  reduc- 
ing the  voltage. 

The  ordinary  incandescent  lamps  operate  at  about  110 
volts  pressure,  although  some  are  built  for  220  volts.  An  elec- 
tric bell  requires  about  2*/2  volts  (a  battery  of  2  cells)  for 
proper  operation. 


12  MODERN   ELECTRICAL  CONSTRUCTION. 

Resistance. 

We  have  seen  that  a  flow  of  current  always  takes  place 
along  or  in  a  conductor.  Every  conductor,  no  matter  how 
large  or  small  it  may  be,  offers  some  resistance  to  this  (low 
of  current  just  as  the  water  pipe  offers  more  or  less  resistance 
to  the  flow  of  water.  This  resistance  may  be  measured  and 
expressed  in  ohms;  the  unit  of  electrical  resistance  being  the 
ohm.  The  ohm  is  defined  as  that  resistance  which  requires  a 
difference  of  potential  of  one  volt  to  send  a  current  of  one 
ampere  through  it.  If  we  should  desire  to  send  a  greater  cur- 
rent through  any  resistance,  we  can  do  so  by  increasing  the 
pressure,  just  as  we  can  increase  the  flow  of  water  in  a  pipe 
by  increasing  the  pressure  or  head  of  water  in  the  tank  that 
supplies  it.  If  the  pressure  is  fixed  we  can  decrease  the 
current  by  using  a  wire  of  greater  resistance  or  increase  it  by 
using  wires  of  lesser  resistance. 

The  ohm  is  the  resistance  of  a  column  of  mercury  106.2 
centimeters  long  (about  Zl/2  feet)  and  one  square  millimetre 
(about  .0015  sq.  in.),  in  cross-section,  at  the  temperature  of 
melting  ice. 

The  resistance  of  a  No.  14  copper  wire  about  380  feet  long 
is  equal  to  one  ohm. 

The  resistance  of  all  conductors  increases  directly  as  the 

\ 


Figure  2 

length  and  decreases  as  the  cross-section  increases.  In  Figure 
2  the  resistance  of  the  two  bars  of  copper  is  exactly  equal. 
Bar  No.  1  having  a  cross-section  of  4  square  inches  and  being 
4  feet  long,  while  bar  No.  2  has  a  cross-section  of  only  1 
square  inch  and  is  only  one  foot  long.  If  bar  No.  1  were 


OHMS   LAW.  13 

reduced  to  a  cross-section  of  1  square  inch,  it  would  become 
16  feet  long  and  would  have  a  resistance  16  times  as  great  as 
that  of  bar  No.  2. 

Current. 

The  electric  current  is  the  result  of  electrical  pressure 
(volts)  acting  through  a  resistance,  and  is  measured  in 
amperes,  the  ampere  being  the  unit  of  current  strength.  The 
ampere  is  defined  as  that  current  which  will  flow  through  a 
resistance  of  one  ohm  when  a  difference  of  potential  or  pres- 
sure of  one  volt  is  maintained  at  its  terminals. 

The  ampere  expresses  only  the  rate  of  flow,  not  the  quan- 
tity. Knowing  the  amperes  if  we  would  know  the  quantity, 
we  must  multiply  by  the  time  that  the  rate  of  flow  continues. 
1  he  rate  of  flow  is  analogous  to  the  speed  of  a  train ;  unless 
we  know  how  long  the  train  is  to  maintain  a  certain  speed,  we 
have  no  idea  how  far  it  is  going. 

Quantity  in  electricity  is  measured  in  coulombs.  The 
coulomb  is  the  quantity  of  current  delivered  by  a  flow  of  one 
ampere  in  one  second. 

Ohm's  Law. 

Ohm's  law  expresses  the  relation  of  the  three  principal 
electrical  units  to  each  other  and  forms  the  basis  of  all  elec- 
trical calculations. 

This  law  states  that  in  any  electric  circuit  (with  direct 
current)  the  current  equals  the  electro-motive  force  divided  by 
the  resistance.  The  current,  we  have  already  seen,  is  the 
medium  which  does  our  work.  Current  flow,  we  see  from  this 
law,  can  be  increased  either  by  increasing  the  electro-motive 
force,  or  electric  pressure,  which  causes  the  flow ;  or  by 
decreasing  the  resistance  which  tends  to  prevent  current  flow. 
Expressed  in  symbols  it  is  this :  I^E/R ;  where  I  stands  for 


14  MODERN   ELECTRICAL  CONSTRUCTION. 

current,  E,  for  electro-motive  force,  and  R  for  resistance.  If, 
as  an  example,  we  have  an  electro-motive  force  (which  we 
shall  henceforth  designate  by  the  customary  abbreviation,  E. 
M.  F.)  of  110  volts  and  a  resistance  of  220  ohms,  the  resulting 
current  will  be  110  divided  by  22Q=l/2  ampere,  being  approxi- 
mately the  current  used  in  a  16  cp.  incandescent  lamp  at  110 
volts.  Thus  it  will  be  seen  that  by  a  very  simple  calculation 
we  can  find  the  current  flow  in  any  conductor  if  we  but  know 
the  E.  M.  F.  and  the  resistance  of  that  circuit. 

This  formula  can  also  be  used  to  find  the  E.  M.  F.,  if  we 
know  the  value  of  current  and  the  resistance,  since  E  divided 
by  R=I ;  I  times  R  must  equal  E.  If  the  current  and  resist- 
ance are  known,  we  need  only  to  multiply  them  together  to  find 
the  E.  M.  F.;  IXR=E.  Knowing  the  current  and  E.  M.  F., 
we  can  find  the  value  of  the  resistance  by  dividing  the  E.  M. 
F.  by  the  current ;  E/I=R. 

As  a  practical  application  of  these  formulas :  If  we  wish 
to  know  how  much  current  a  certain  E.  M.  F.  can  force 
through  a  certain  resistance,  we  must  divide  the  E.  M.  F. 
(volts)  by  the  resistance  (ohms.)  If  we  wish  to  know  what 
E.  M.  F.  (volts)  will  be  necessary  to  force  a  certain  cur- 
rent (amperes)  through  a  certain  resistance,  we  need  only 
multiply  the  current  (amperes)  to  be  obtained  by  the  resist- 
ance in  ohms.  If  we  wish  to  know  how  much  resistance 
(ohms)  must  be  placed  in  a  circuit  to  keep  down  the  current 
flow  to  a  certain  limit,  we  need  only  divide  the  E.  M.  F. 
(volts)  by  the  desired  current  (amperes)  ;  the  result  will  be 
the  value  in  ohms  of  the  required  resistance. 

Power. 

The  power  consumed  or  transmitted  in  an  electric  cir- 
cuit equals  the  product  of  the  volts  and  amperes;  pressure 
and  current. 


POWER.  15 

To  find  the  power  of  a  steam  engine,  we  must  know  the 
pressure  of  the  steam  and  the  quantity  used ;  the  power  con- 
tained in  the  water  of  a  dam  depends  upon  its  volume  and  its 
head.  The  power  we  can  obtain  from  the  wind  depends  upon 
its  speed  and  the  surface  we  expose  to  it  which  also  measures 
the  quantity. 

All  of  these  cases  are  analogous  and  similar.  Power  ex- 
presses the  rate  of  doing  work,  thus  the  rate  of  work  is  the 
same  whether  we  are  lifting  one  pound  at  the  rate  of  100 
feet  per  minute,  or  100  pounds  at  the  rate  of  one  foot  per 
minute.  The  unit  of  electrical  power  is  the  watt.  It  is  the 
power  expended  in  an  electric  circuit  when  one  ampere  flows 
through  a  resistance  9f  one  ohm,  or  when  a  difference  of 
potential  of  one  volt  is  maintained  in  a  circuit  having  a  resist- 
ance of  one  ohm.  In  an  electric  light  circuit,  for  instance, 
as  far  as  the  power  is  concerned,  it  is  immaterial  whether 
each  lamp  requires  110  volts  and  l/z  ampere,  or  55  volts  and 
one  ampere,  or  220  volts  and  %  ampere.  The  power  (watts) 
expended  in  an  electric  circuit  is  always  equal  to  the  volts 
multiplied  by  the  amperes;  thus,  one  ampere  at  1,000  volts 
is  equal  to  100  amperes  at  10  volts,  or  to  200  amperes  at  5 
volts.  In  any  power  transmission  whenever  the  pressure 
(volts)  is  lowered,  the  current  (amperes)  must  be  increased 
or  the  power  (watts)  will  fall  off,  and,  on  the  other  hand, 
whenever  the  pressure  is  increased  the  current  may  be 
decreased. 

Instead  of  multiplying  volts  by  amperes,  we  can  find  the 
power  in  an  electric  light  circuit  by  multiplying  the  current  by 
itself  and  then  by  the  resistance ;  or  the  E.  M.  F.  by  itself  and 
divide  by  the  resistance. 

Thus  knowing  the  volts  and  the  amperes,  we  use  the 
.  formula  E  X  I=W.  Knowing  only  the  amperes  and  the 
ohms,  we  may  use  the  formula,  I2  X  R  =  W ;  and  lastly, 


16  MODERN   ELECTRICAL  CONSTRUCTION. 

knowing    only    the    volts    and    ohms,    we    use    the    formula, 


. 

In  the  above  E  stands  for  E.  M.  R,  or  volts;  I  for  current 
or  amperes;  and  R  for  resistance  or  ohms.  _ 

Divided  Circuits. 

Currents  of  electricity  always  flow  along  the  paths  of 
least  resistance  just  as  currents  of  water  do.  Water,  it  is 
well  known,  will  not  flow  over  the  top  of  a  mill  dam  while 


ii 


Figure  3 

there  is  an  opening  alongside  of  it  through  which  it  can  flow. 
If  a  barrel  of  water  be  provided  with  two  openings,  one 
large  opening  and  one  small,  a  much  larger  quantity  will 
flow  out  through  the.  large  opening  than  through  the  small. 
This  is  because  the  resistance  to  the  flow  of  water  of  the 
large  opening  is  so  much  less  than  the  resistance  of  the 
small  opening. 

An  electric  current  will  act  in  just  the  same  way;  the 
conductor  having  the  lesser  resistance  will  carry  the  greater 
current.  If  we  know  the  resistances  of  the  different  paths 
open  to  a  certain  current  we  can  determine  to  a  nicety  how 
much  current  will  flow  in  each.  In  Figure  3,  which  repre- 
sents diagramatically  a  battery  of  two  cells  and  an  electric 
circuit,  the  resistance  of  the  two  paths,  a  and  b,  is  equal  to 


DIVIDED  CIRCUITS.  17 

10  ohms  each,  and  the  current  will  divide  equally  between 
them.  If  the  resistance  of  a  were  5  ohms,  and  that  of  b, 
10  ohms,  two-thirds  of  the  total  current  would  pass  through 
a  and  the  one-third  through  b. 

In   all   such   divided   circuits,   the   current   is   always   in- 
versely proportional  to  the  resistance  and  the  simplest  way 
>  find  the  current  in  each  is  to  add  the  resistances  of  the  two 
circuits;    for   instance .  as   above,   5   plus    10  equals    15;    now 
15  of  this  current  will  flow  through  the  10  ohms  and  10/15 
of  the  current  will  flow  through  the  5  ohms. 

To  determine  the  combined  resistance  of  the  two  wires 
a  and  b,  we  need  simply  to  consider  them  as  made  into  one 
wire.  If  they  are  both  alike,  they  would,  if  made  into  one 
wire,  be  twice  as  large  as  either  one  is  at  present,  and  would 
then  have  only  one-half  as  much  resistance  as  either  one  had 
before;  for  the  resistance  of  any  conductor  increases  directly 
as  its  length,  and  decreases  as  the  cross-section  increases 
Hie  combined  resistances  of  any  two  conductors  can  be  found 
by  multiplying  their  two  resistances  together  and  dividing 
this  product  by  their  sum.  Thus,  again  taking  the  value 
of  a  and  b  as  10  ohms  each,  10X10  equals  100,  this  divided 
10  plus  10  equals  5,  which  is  the  combined  resistance  of  the 


two. 


If  we  have  a  large  number  of  branch  circuits  as  shown  in 
Figure   4,   which   represents   diagramatically   an   incandescent 


Figure  4 


electric  light  circuit  of  12  lights  (which  is  equal  to  12  separate 

:ircuits,  since  each  lamp  really  forms  a  circuit  by  itself),  we 

can  find  the  joint  resistance  of  the  12  by  proceeding  as  before; 

t  is,  multiplying  together  the   resistance  of  the  first  and 


18  MODERN  ELECTRICAL  CONSTRUCTION. 

second  lamp  and  dividing  by  the  sum  of  these  resistances ;  next 
take  the  result  so  obtained  (which  is  the  combined  resist- 
ance of  the  first  two  lamps)  and  with  it  multiply  the  resist- 
ance of  the  third  lamp  and  divide  by  the  sum  as  before.  By 
repeating  this  operation  and  always  treating  the  joint  resist- 
ances already  found  as  one  circuit,  the  joint  resistance  of  any 
number  of  such  circuits  can  be  found.  Another  and  a  very 
much  quicker  way  consists  in  using  the  following  formula : 
The  joint  resistance  of  any  number  of  parallel  circuits  is 
equal  to  the  reciprocal  of  the  sum  of  the  reciprocals.  The 
reciprocal  of  any  number  is  1  divided  by  that  number.  If  we 
have  three  circuits,  having  respectively  10,  20,  and  30  ohms 
resistance,  we  proceed  in  the  following  way:  The  reciprocal 
of  10  is  1/10,  of  20,  1/20,  etc.,  the  joint  resistance,  there- 
fore, is  1/10  plus  1/20  plus  1/30  equals  11/60,  and  1  divided 
by  this  number  which  is  5  5/11. 

These  methods  are  only  necessary  when  the  resistances 
are  of  different  values.  When  all  of  them  are  alike,  as  is 
usual  with  incandescent  lights,  the  resistance  of  one  lamp 
needs  only  to  be  divided  by  the  number  of  lamps  to  find  the 
joint  resistance.  Thus,  supposing  each  of  the  12  lamps  to 
have  a  resistance  of  220  ohms,  the  joint  resistance  of  the 
circuit  would  be  220/12=181/3. 


CHAPTER  II. 
Electric  Bells. 

We  are  now  in  a  position  to  apply  the  electrical  laws  we 
have  just  discussed  practically,  and  for  this  purpose  may 
take  up  electric  bells  and  bell  circuits. 

Figure  5  shows  an  electric  bell,  push  button  and  battery, 
all  connected  up  and  complete.  The  action  of  the  bell  when 


Figure  5 


fully  connected  is  as  follows:  Pressing  the  push  button 
closes  the  circuit  and  current  at  once  flows  from  the  carbon 
pole  marked  +  through  the  push  button  to  the  binding  post 
A  on  the  bell  frame,  thence  along  the  fine  wire  W  to  the 
iron  frame-work  supporting  the  armature,  B.  This  frame- 


20  MODERN   ELECTRICAL  CONSTRUCTION. 

work  is  in  electrical  connection  with  B.  The  armature,  B, 
is  provided  with  contact  spring  S,  which  normally  rests 
against  the  adjusting  screw,  C.  The  current  now  passes  from 
the  contact  spring  to  the  adjusting  screw  and  from  it  to  the 
wire  wound  on  the  magnets,  M,  around  the  many  turns  of 
wire  to  the  binding  post,  D,  and  back  to  the  zinc  pole  of  the 
battery  marked  — . 

The  current  circulating  many  times  in  the  wire  wound  on 
the  spools  of  M  makes  the  iron  cores  magnetic  so  that  they 
now  attract  the  armature  B.  When  this  armature  is  at- 
tracted, it  moves  towards  the  magnets,  M,  and  carries  the 
small  contact  spring  with  it,  thus  breaking  the  connection  be- 
tween C  and  S. 

This  stops  the  current  flow  and  the  magnets,  M,  are  at 
once  demagnetized,  thus  releasing  the  armature  B,  which 
flies  back  and  again  clores  the  circuit  at  CS,  this  causes  the 
armature  to  be  attracted  again  and  once  more  the  circuit  is 
broken.  In  this  way  the  armature  is  made  to  strike  the  gong 
continuously  while  the  circuit  is  kept  closed  at  the  push  button. 
When  the  button  is  released,  the  circuit  is  permanently  open 
and  the  bell  at  rest. 

In  the  figure  there  is  shown  only  one  cell,  this,  if  a  good 
form  is  selected,  is  sufficient  for  a  new  bell  if  the  circuit  is 
not  long.  When,  however,  the  bell  is  used  much  the  contact 
points  are  eaten  away  by  the  little  sparks  occurring  every  time 
the  bell  breaks  the  circuit.  Dirt  is  also  likely  to  gather  on 
them  and  prevent  good  contact  being  made.  Both  of  these 
factors  add  resistance  to  the  circuit,  and  consequently 
lessen  the  current  flow. 

We  have  seen  before  that  the  current  equals  the  E.  M. 
F.  divided  by  the  resistance,  and  in  order  to  obtain  the 
necessary  current  flow  to  operate  the  bell,  we  may  either 
clean  the  contact  points  to  lessen  the  resistance,  or  increase 
the  E.  M.  F.  by  adding  another  cell  in  series  with  the  first. 


ELECTRIC   BELLS. 


21 


The  latter  expedient  is  by  far  the  better,  because  it  gives 
us  a  little  surplus  of  power  which  is  very  useful  to  over- 
come variations  in  adjustment  of  the  contact  spring,  loose 
contacts,  dirt,  etc.  We  should  avoid  using  too  many  cells 
as  well  as  not  enough.  If  too  many  cells  are  used,  there 


Or 

n 


Or 

n 


,777 


Figure  6 

will  be  much  unnecessary  damage  done  to  contact  points  by 
the  larger  sparks. 

If  the  circuit  is  very  long,  the  great  length  of  wire  will 
also  provide  additional  resistance.  This  can  be  overcome  in 
two  ways,  by  increasing  the  E.  M.  F.  as  above,  or  by  using 
larger  wires.  We  have  already  seen  that  the  larger  the  wire, 
the  less  will  be  its  resistance.  It  is  common  practice  to  use 


22  MODERN   ELECTRICAL  CONSTRUCTION. 

No.  18  copper  wire  for  all  ordinary  distances  and  for  single 
bells.  With  large  bell  systems,  it  is  customary  to  use  No.  16 
or  14  for  the  main  wire,  which  leads  to  all  of  the  bells  and 
may  be  called  upon  to  supply  several  bells  at  the  same  time. 
Figure  6  shows  a  diagram  of  such  a  system  and  in  case  the 
three  push  buttons  are  used  at  the  same  time,  three  times  as 
much  current  will  flow  in  the  main  or  battery  wire  a  as  in 
either  of  the  other  wires. 

We  have  seen  before  that  currents  of  electricity  divide 
among  different  circuits  in  the  inverse  ratio  of  their  resist- 
ances. In  other  words,  the  circuit  having  the  least  resistance 
will  carry  the  most  current.  If  our  bell  system,  Figure  6, 
be  "grounded"  at  the  two  points  x  and  y  (i.  e.,  bare  wire  in 
contact  with  metal  parts  of  buildings  which  are  connected 
together)  the  current  instead  of  flowing  through  the  longer 
circuit  and  the  bell,  will  flow  through  the  short  circuit  and 
leave  it  impossible  to  operate  the  bells.  If  the  contacts,  at 
x  and  y  are  poor,  i.  e.,  of  high  resistance,  only  a  small  part 
of  the  current  will  leak  from  one  to  the  other.  In  such  a 
case,  the  bells  may  work  properly,  but  the  battery  will  soon 
run  down  and  there  is  a  strong  likelihood  that  one  of  the 
wires  will  be  eaten  away  through  electrolytic  action.  To 
prevent  troubles  of  this  kind,  bell  wires  should  be  well  in- 
sulated and  kept  away  from  pipes  or  metal  parts  of  building. 
Damp  places  should  also  be  avoided  and  special  care  is 
recommended  for  the  battery  wire  a,  Figure  6.  For  further 
information  concerning  diagrams,  etc.,  of  bell  circuits  the 
reader  is  referred  to  Wiring  Diagrams  and  Descriptions  by 
the  authors  of  this  work,  Fred  J.  Drake  &  Co.,  Chicago. 

Bell  wires  are  usually  run  along  base  boards,  over  picture 
mouldings,  etc.,  in  some  cases  they  are  also  fished  as  explained 
further  on.  Batteries  should  be  located  in  cool,  dry  places, 
where  they  are  not  liable  to  freeze,  and  where  they  are 
readily  accessible  as  they  must  be  kept  nearly  full  of  water 
and  must  be  recharged  from  time  to  time. 


23 


The  Telephone. 


The  principle  and  action  of  the  Bell  telephone  can  be  best 
explained  by  reference  to  Figure  7.  In  this  figure,  A  repre- 
sents the  transmitter,  and  B,  the  receiver.  The  essential 
parts  of  the  transmitter  are:  the  diaphragm,  a;  an  electric 
circuit,  containing  a  battery,  b,  and  consisting  of  the  wires, 
c,  c1  and  partly  wound  upon  an  iron  core,  d. 

This  electric  circuit,  it  will  be  seen  from  the  figure,  con- 
nects with  one  pole  to  the  diaphragm,  a,  and  with  the  other 
to  a  small  metal  plate,  e.  Between  the  diaphragm,  a  (which 
is  a  plate  of  very  thin  iron),  and  the  plate,  c,  there  are  many 
small  pieces  of  carbon  which  complete  the  circuit.  When 
now  a  party  speaks  into  the  mouthpiece  of  the  transmitter, 


Figure  7 


the  sound  waves  cause  the  diaphragm,  a,  to  vibrate;  the  rate 
of  vibration  and  character  of  the  vibrations  being  an  exact 
duplication  of  the  voice  speaking  into  it.  These  vibrations 
cause  the  small  pieces  of  carbon  between  the  diaphragm  and 
the  back  plate  to  be  alternately  compressed  and  allowed  to 
expand.  Now  the  resistance  of  these  carbon  pieces  is  de- 
creased as  they  are  tightly  pressed  together,  and  again  in- 
creased when  the  pressure  is  released.  Therefore  the  cur- 
rent of  electricity  flowing  through  them  varies  continuously 
while  the  diaphragm  is  in  motion. 

This    varying   current    circulates    around    the    lower   part 
of  the  iron  core,  d,  and  the  two  windings  upon  it  form  an 


24 


MODERN   ELECTRICAL  CONSTRUCTION. 


ordinary  induction  coil.  Every  variation  of  current  strength 
in  the  circuit  of  the  transmitter  is  by  means  of  it  reproduced 
in  the  circuit  of  the  receiver,  B. 

The  essential  parts  of  the  telephone  receiver  are:  The 
diaphragm  f,  very  similar  to  that  of  the  transmitter,  the  two 
magnets,  g,  and  the  electric  circuit  coming  from  the  induction 
coil  of  the  transmitter.  The  electric  circuit,  we  have  already 
seen,  is  traversed  by  electric  currents  exactly  like  those  that 
flow  in  the  circuit  of  the  transmitter.  These  currents  pass 
around  electro-magnets,  g,  and  attract  the  diaphragm,  /, 
more  or  less  strongly  in  proportion  to  the  varying  degrees  of 
current  strength. 

In  this  manner  the  diaphragm,  /,  of  the  receiver  is  made 
to  vibrate  in  exact  unison  with  that  of  the  transmitter,  and 
thus  to  reproduce  exactly  the  sounds  given  to  the  trans- 
mitter. 

The  transmitter   is   not  absolutely  necessary   for  the   re- 


Figure  8 

ceiver  can  be  used  as  such,  and  in  fact  was  so  used  at  first. 
Lines  of  short  distances  can  be  operated  without  transmit- 
ters, but  the  speech  will  not  be  as  plain. 


INDUCTION   COIL. 


25 


Figure  8  is  a  diagram  of  the  connections  of  two  telephone 
instruments  together  with  the  necessary  call  bells.  When  the 
lines  are  not  in  use,  the  receivers,  a,  are  hanging  on  the 
hooks,  h,  holding  them  down  as  shown  by  dotted  lines.  This 
leaves  the  circuit  complete  through  the  earth,  g,  magneto 
generator,  e,  bell  f,  line  i,  and  duplicates  of  these  parts  at  the 
right.  When  now  the  magneto  generator  is  operated  both 
bells  will  ring.  When  the  receivers  are  removed,  a  spring 
forces  the  hook  upwards  making  the  connection  shown  in 
solid  lines.  This  closes  the  battery  circuit  which  must  be 
open  when  the  instrument  is  not  in  use  or  the  battery  will 
run  down. 

The  talking  circuit  is  now  complete  from  earth,  g,  through 
the  receiver,  a,  induction  coil,  b,  line  i,  and  duplicates  of  these 
parts  at  the  right. 

The  Induction  Coil. 

Figure  9  is  a  diagramatic  illustration  of  an  induction 
coil  as  used  mostly  by  medical  men.  Such  an  instrument 


Figure  9 

consists  of  an  iron  core,  B,  usually  made  up  of  a  number 
of  soft  iron  wires;  and  two  electrical  circuits  insulated  from 
each  other,  and  terminating  in  the  two  pair  of  binding  posts, 
A  and  D.  Of  these  two  circuits  A  consists  of  a  short  length 


26  MODERN   ELECTRICAL  CONSTRUCTION. 

of  comparatively  heavy  wire  wound  upon  the  iron  core,  and 
is  known  as  the  primary  coil.  D  is  a  similar  coil,  but  usually 
consisting  of  many  more  turns  of  wire,  and  the  wire  is  also  of 
much  smaller  gauge  and  is  known  as  the  secondary  coil. 

The  operation  is  as  follows :  A  battery  is  connected  to  the 
binding  posts,  A,  and  current  begins  to  flow  in  the  circuit.  In 
this  circuit  is  an  interrupter  or  vibrator,  E,  constructed 
similarly  to  the  one  described  in  connection  with  the  electric 
bell.  As  current  flows  through  the  primary  coil,  it  mag- 
netizes the  core,  B,  and  this  attracts  the  armature,  E,  causing 
it  to  break  the  connection  between  itself  and  the  adjusting 
screw.  As  this  connection  is  broken,  the  current  in  A  ceases 
to  flow,  the  core  is  de-magnetized  and  the  armature  again 
connects  with  the  adjusting  screw.  This  action  is  repeated 
just  as  in  the  electric  bell,  and  in  consequence  the  core  B, 
is  rapidly  magnetized  and  de-magnetized.  . 

Every  time  the  core,  B,  is  magnetized  a  current  of  electric- 
ity, lasting,  however,  only  an  instant,  is  induced  in  the  second- 
ary coil,  D.  The  magnetism  in  the  core  is  caused  by  a  cur- 
rent of  electricity  circulating  around  it,  and  currents  of 
electricity  are  in  turn  produced  by  this  magnetism  in  the 
other  or  secondary  coil. 

This  method  of  producing  electric  currents  is  known  as 
electro-magnetic  induction,  and  currents  so  produced  are  said 
to  be  "induced"  currents,  hence  the  name  induction  coil.  The 
currents  so  induced  are  alternating,  that  is,  changing  in 
direction.  At  the  "making"  of  the  primary  circuit,  the  cur- 
rent in  the  secondary  coil  is  in  a  direction  which  opposes  the 
magnetization  of  the  core  by  the  primary  current;  at  the  time 
of  "break"  in  the  primary  circuit,  the  induced  current  will  be 
in  the  opposite  direction. 

The  tube,  C,  is  movable  and  may  be  slipped  entirely  in  over 
the  iron  core,  or  withdrawn. entirely.  If  it  is  in,  the  currents 
which  were  before  being  induced  in  the  secondary  wires  are 


BATTERIES  27 

now  induced  in  the  metal  of  the  tube  and  consequently  the 
effect  on  the  secondaries  is  very  much  reduced. 

The  energy  in  the  primary  and  secondary  coils  is  always 
equal.  If  the  two  coils  have  the  same  number  of  turns,  the 
currents  and  electro-motive  forces  are  exactly  alike.  If  the 
secondary  coil  has  more  turns  of  wire  than  the  primary, 
the  induced  E.  M.  F.  in  it  will  be  greater,  but  the  current 
will  be  smaller  and  vice  versa.  The  induction  coil  is  very 
similar  to  the  alternating  current  transformer,  the  main 
difference  being  that  the  transformer  does  not  have  an  in- 
terrupter since  the  current  supplied  to  it  is  itself  constantly 
alternating. 

Batteries. 

Currents  of  electricity  for  commercial  purposes  are  pro- 
duced either  by  dynamo  electric  machines  or  by  batteries. 

A  "battery"  is  the  name  given  to  a  number  of  cells  con- 
nected together  so  as  to  produce  a  current  greater  than  one 


Figure  10  Figure  11 

cell  alone  could  produce.  Figure  10  shows  one  cell  of  a  kind 
that  is  generally  used  only  intermittently,  as  for  instance  with 
door-bells.  When  the  bell  is  not  ringing  the  battery  is  idle. 


28  MODERN   ELECTRICAL  CONSTRUCTION. 

This  style  of  cell  is  very  useful  for  such  work,  but  entirely 
useless  for  work  requiring  current  continuously.  The  cell 
consists  of  a  glass  jar  which  is  filled  about  Y*  full  of  water 
in  which  a  quantity  of  sal-ammoniac  is  dissolved.  Immersed  in 
this  solution  is  a  carbon  cup  or  center,  which  forms  the 
positive  or  +  pole  of  the  cell,  and  a  zinc  rod,  carefully 
separated  from  the  carbon  by  a  rubber  washer  at  the  bottom 
and  a  porcelain  tube  at  the  top.  So  arranged,  the  current  tends 
to  flow,  in  the  battery,  from  the  zinc  to  the  carbon  and  if  the 
zinc  and  carbon  outside  of  the  cell  be  joined  by  a  piece  of 
wire  or  other  conductor  of  electricity,  the  current  will  flow 
in  the  external  circuit,  from  the  carbon  back  to  the  zinc.  If 
the  zinc  and  carbon  are  not  joined  by  a  conductor  of  electric- 
ity there  will  be  no  current  flow,  but  merely  an  electrical  pres- 
sure tending  to  send  a  current.  Each  cell  of  this  kind  has 
an  electro-motive  force  of  about  1.4  volts.  This  is  not  suffic- 
ient for  general  use  in  connection  with  bells,  etc.,  and  in 
order  to  obtain  greater  current  strength  a  number  of  cells 
are  connected  together  in  series  as  shown  in  Figure  11. 

This  figure  shows  a  different  kind  of  cell,  but  will  never- 
theless illustrate  the  method  of  connecting  cells  in  series; 
which  is,  to  connect  the  carbon  or  copper  pole  of  the  first 
cell  to  the  zinc  of  the  second,  and  again  the  carbon  pole  of  the 
second  to  the  zinc  of  the  third,  continuing  in  this  way  through 
all  of  the  cells.  Thus  connected,  all  of  the  electro-motive 
forces  act  in  one  direction  and  if  we  have  twelve  cells  each 
of  an  electro-motive  force  of  1.4  volts,  we  obtain  a  total 
electro-motive  force  to  apply  on  our  work  of  12  X  1.4  or  16.8 
volts. 

Should  we,  however,  connect  six  of  the  twelve  cells  as 
above,  and  then  accidentally  connect  the  other  six  in  the 
opposite  direction,  that  is,  the  zinc  of  the  sixth  cell  to  the 
zinc  of  the  seventh,  and  then  continue  in  this  order,  we  should 
obtain  no  current  whatever;  six  of  our  cells  would  tend  to 


BATTERIES.  29 

send  current  in  one  direction  and  six  in  the  other,  so  that  the 
result  would  be  nothing.  Should  ten  cells  be  properly  con- 
nected to  send  current  in  one  direction  and  two  connected 
to  oppose  them,  the  net  electro-motive  force  would  be  10  X  1.4 
minus  2  X  1.4,  which  is  11.2.  The  ten  cells  would  force  current 
through  the  other  two  in  the  opposite  direction. 

The  electro-motive  force  of  a  cell  is  independent  of  its 
size,  that  is,  a  very  small  cell  would  set  up  just  as  high  an 
electrical  pressure  as  a  very  large  one  made  of  the  same 
material.  A  large  cell  is,  however,  capable  of  delivering  a 
much  stronger  current  because  its  own  resistance  to  the  cur- 
rent flow  is  much  less  than  that  of  a  small  cell.  Large  cells 
will,  therefore,  in  most  cases  give  very  much  better  service 
than  small  ones.  Especially  in  cases  where  considerable 
current  is  required  as  in  electric  gas-lighting  and  annunciator 
work,  where  it  is  always  possible  that  two  or  three  bells  or 
fixtures  may  be  called  into  action  at  the  same  time. 

In  setting  up  and  maintaining  sal-ammoniac  batteries,  the 
following  general  rules  should  be  observed : 

Use  only  as  much  sal-ammoniac  as  will  readily  be  dis- 
solved; if  any  settles  at  the  bottom  it  shows  that  too  much 
has  been  used.  Keep  your  battery  in  a  cool  place,  but  do 
not  allow  it  to  freeze.  See  that  the  jars  are  always  about 
M  full  of  water. 

Keep  the  tops  of  glass  jars  covered  with  paraffir  to 
prevent  salts  from  creeping. 

The  battery  should  never  be  allowed  to  remain  in  action 
(i.  e.,  send  current)  continuously,  or  it  will  run  down.  If 
it  has  been  run  down  through  a  short  circuit  or  other  cause, 
it  should  be  left  in  open  circuit  for  several  hours ;  it  will  then 
usually  "pick  up"  again. 

The  so-called  dry-batteries  are  made  up  of  about  the 
same  material,  but  applied  in  form  of  a  paste.  They  are 


30  MODERN   ELECTRICAL  CONSTRUCTION. 

suitable  for  the  same  kind  of  work  and  especially  handy  for 
portable  use. 

For  continuous  current  work,  such  as  telegraphy,  for 
instance,  the  kind  of  battery  shown  in  Figure  11  is  generally 
used.  The  electro-motive  force  of  this  style  of  battery  is  a 
little  less  than  that  of  the  sal-ammoniac  battery  and  its  re- 
sistance is  considerably  greater. 

Therefore,  it  is  not  well  adapted  for  work  requiring  con- 
siderable current  strength.  Bells,  telegraph  instruments,  etc., 
to  be  used  with  this  battery  require  to  be  specially  designed 
for  it;  the  current  being  less  in  quantity  must  be  made  to 
circulate  around  the  magnets  many  jnore  times  in  order  to 
fully  magnetize  them. 

The  sal-ammoniac  batteries  cannot  be  used  continually  or 
they  will  run  down ;  this  battery  must  be  kept  at  work  always 
or  it  will  deteriorate. 

This  style  of  cell  is  known  as  the  crow-foot  or  gravity 
cell,  the  action  of  gravity  being  depended  upon  to  separate 
the  essential  elements  of  the  solution. 

To  set  up  this  battery,  the  zinc  crow-foot  is  suspended 
from  the  top  of  the  glass  jar  as  shown.  The  other  element 
of  the  cell  consists  of  copper  strips  riveted  together  and 
connected  to  a  rubber-covered  wire  shown  at  the  left  of  each 
cell,  Figure  11.  This  copper  is  spread  out  on  the  bottom  of 
the  jar  and  clear  water  poured  in  until  it  covers  the  zinc. 
Next  drop  in  small  lumps  of  blue  vitriol,  about  six  or  eight 
ounces  to  each  cell. 

The  resistance  may  be  reduced  and  the  battery  be  made 
immediately  available  by  drawing  about  half  a  pint  of  the 
upper  solution  from  a  battery  already  in  use  and  pouring  it 
intq  the  jar;  or,  when  this  cannot  be  done,  by  putting  into 
the  liquid  four  or  five  ounces  of  pulverized  sulphate  of  zinc. 

Blue  vitriol  should  be  dropped  into  the  jar  as  it  is  con- 
sumed, care  being  taken  that  it  goes  to  the  bottom.  The 


BATTERIES.  31 

need  of  the  blue  vitriol  is  shown  by  the  fading  of  the  blue 
color,  which  should  be  kept  as  high  as  the  top  of  the  copper, 
but  should  never  reach  the  zinc. 

A  battery  of  this  kind  when  newly  set  up  should  be  short 
circuited  for  a  few  hours,  that  is,  a  wire  should  be  con- 
nected from  the  zinc  at  one  end  of  the  battery  to  the  copper 
at  the  other. 

There  are  many  styles  of  batteries  and  different  chemicals 
are  used  with  them.  The  two  kinds  above  described  are, 
however,  the  most  used.  The  methods  of  connecting  is  in 
all  batteries  the  same. 

Figure  12  shows  a  diagram  of  a  battery  connected  in 
series;  the  long  thin  lines  repre- 
sent the  copper  or  carbon  pole 
from  which  the  current  flows  in 
the  external  circuit  and  the  short 
thick  lines  represent  the  zinc  from 
Figure  12  which  the  current  flows  toward 

the  copper  inside  of  the  cell. 

If  we  have  a  circuit  of  low  resistance  to  work   through 

and  desire  to  increase  the  current,  we  may  group  our  cells  as 

r-jf  —  i  —  -  nas  -  «^n     shown    in    Figure    13,    where   two 

£  fm  I     sets  are  in  parallel.     This  arrange- 

~zr  ~  ment  will  give  a  stronger  current, 

-         -  but  it  is  necessary  to  see  that  both 

groups    of    cells    have    the    same 

P^t-     "H        K»  _  3^1     electro-motive  force;  if  they  have 


Figure  13  not    tjie  higher  one  will  send  the 

current  through  the  lower.  If  the  two  batteries  are  not  con- 
nected with  similar  poles  together,  they  would  be  on  short  cir- 
cuit, and  no  current  could  be  obtained  in  the  external  circuit. 


CHAPTER  III. 

Wiring  Systems. 

There  are  numerous  systems  of  electric  light  distribution. 
The  oldest  and  the  first  to  come  into  general  use  is  shown 
diagramatically  in  Figure  14.  This  is  the  series  arc  system. 
In  this  system  the  same  current  passes  through  all  of  the 
lamps;  and  as  more  or  less  lamps  are  required  the  E.  M.  F. 
of  the  dynamo  must  be  correspondingly  increased  or  dimin- 


Figure  14 

ished.  This  is  accomplished  by  means  of  an  automatic 
regulator  connected  to  the  dynamo. 

The  current  used  with  this  system  seldom  exceeds  ten 
amperes  and  large  wires  are  never  required.  This  system  is 
best  suited  for  street  lighting  where  long  distances  are  to  be 
covered. 

In  these  diagrams,  D  represents  the  dynamo,  and  F, 
the  "field"  coils  of  the  dynamo.  With  constant  current 
systems  the  "fields"  are  usually  in  series  with  the  armature 
of  the  dynamo,  as  shown  in  Fig.  14,  and  the  lamps,  so 
that  the  same  current  must  pass  through  all.  With  constant 


WIRING    SYSTEMS.  33 

potential  systems,  the  field  coils  are  generally  independent  of 
the  rest  of  the  circuit.  With  such  systems  the  current  used 
in  the  circuit  is  so  variable  that  it  cannot  be  used  in  the 
fields. 

Another  system,  known  as  the  multiple  arc  or  parallel 
system,  is  shown  in  Figure  15.  In  this  system  the  E.  M. 
F.  never  varies,  but  the  current  is  always  proportional  to  the 


Figure  15 

number  of  lights  used.  If,  for  instance,  only  one  light  is  used, 
there  is  a  current  of  about  one-half  ampere,  but  if  ten  16 
cp.  lights  are  used  there  must  be  a  current  of  about  five 
amperes.  Where  many  lights  are  used  with  this  system,  the 
main  wires  require  to  be  quite  large,  and  must  always  be 
proportional  to  the  number  of  lights.  This  system  is  oper- 
ated usually  at  110  volts  and  is  suitable  for  residences,  stores, 
factories  and  all  indoor  illumination.  It  is  not  well  adapted 
to  the  transmission  of  light  and  power  over  long  distances. 
The  3-wire  system  shown  in  Figure  16  combines  many  of 


Figure  16 

the  advantages  of  both  the  foregoing  systems.  As  will  be 
seen  from  the  diagram,  it  consists  of  two  dynamos  connected 
in  series  and  a  system  of  wiring  of  one  positive  +,  one  nega- 
tive —  and  a  neutral  =  wire.  So  long  as  an  equal  number  of 


34  -MODERN    ELECTRICAL   CONSTRUCTION. 

lights  are  burning  on  both  sides  of  the  neutral  wire,  this 
wire  carries  no  current,  but  should  more  lights  be  in  use 
on  one  side  of  the  system  than  on  the  other,  the  neutral  wire 
will  be  called  upon  to  carry  the  difference.  If  all  the  lights 
on  one  side  are  out,  the  dynamo  on  that  side  will  be  running 
idle. 

The  currents  in  the  neutral  wire  may  be  either  positive 
or  negative  in  direction.  The  principal  advantage  of  this  sys- 
tem is  that  with  it  double  the  voltage  of  the  2-wire  systems 
is  employed  and  yet  the  voltage  at  any  lamp  is  no  greater  than 
with  the  use  of  two  wires.  It  is  customary  to  use  110  volts 
on  each  side  of  the  neutral  wire  and  this  gives  a  total  volt- 
age over  the  two  outside  wires  of  220  volts.  As  the  same 
current  passes  ordinarily  through  two  lamps  in  series,  we 
need,  for  a  given  number  of  lamps  only  half  as  much  current 
as  with  2-wire  systems  and  can,  therefore,  use  smaller 
wires.  For  the  same  number  of  lights  and  the  same  per- 


Figure  17 

centage  of  loss  the  amount  of  copper  required  in  the  two 
outside  wires  is  only  one-fourth  that  of  2-wire  systems;  to 
this  must  be  added  a  third  wire  of  equal  size  for  the  neutral, 
so  that  the  total  amount  of  copper  required  with  this  system 
is  y%  of  that  of  2-wire  system  using  the  same  kind  of  lamps. 
Incandescent  lamps  are  often  run  in  multiple-series,  as  in 


WIRING   SYSTEMS. 


Figure  17,  without  a  neutral  wire.  The  number  of  lamps  to 
be  used  in  series  depends  upon  the  voltage  of  the  dynamo. 
If  that  is  550,  five  110  volt  lamps  are  required  in  each  group, 
or  ten  55  volt  lamps. 

If  the   filament  of  one   lamp   breaks  all  of  the  lamps   in 


Figure  18 

that  group  are  extinguished  and  if  one  is  to  be  used  all  must 
be  used. 

Figure  18  shows  the  diagram  of  a  series-multiple  system. 
This  style  of  wiring  should  be  avoided. 

A  diagram  of  an  alternating  current  system  is  shown  in 


Figure  19 

Figure  19.     In  this  system  extremely  high  voltage  is  used  and 
consequently  the  currents  are  never  very  great.     This  makes 


36  MODERN   ELECTRICAL  CONSTRUCTION. 

it  extremely  useful  for  long  distance  transmission.  Since, 
however,  the  high  pressure  employed  cannot  be  used  directly 
in  our  lamps  it  must  be  transformed  into  lower  pressure. 
This  is  done  by  means  of  transformers,  and  it  is  possible  to 
reduce  the  line  voltage  to  any  desirable  extent.  As  the  volt- 
age is  reduced,  however,  the  current  increases  and  the  wires 
taken  from  the  transformers  into  the  buildings  must  be  as 
large  as  those  for  2-wire  systems  using  the  same  kind  of 
lamps.  The  high  pressure,  or  primary  wires,  are  rarely 
allowed  inside  of  buildings. 


The  Transmission  of  Electrical  Energy. 

We  have  seen  that  currents  of  electricity  flow  only  in 
electrical  conductors,  and  that  these  conductors  are  usually 
arranged  in  the  form  of  wires.  We  have  further  seen  that 
the  power  transmitted  is  proportional  to  the  product  of  the 
volts  and  amperes  used.  The  actual  amount  of  energy  trans- 
mitted being  the  product  of  the  above  multiplied  by  the  time. 

Currents  of  electricity  always  encounter  some  resistance 
and  in  consequence  of  this  resistance,  generate  heat;  the 
generation  of  heat  in  any  electric  circuit  being  proportional 
to  the  square  of  the  current  multiplied  by  the  resistance. 
This  formula,  I2  X  R  expresses  the  loss  of  electrical  energy 
due  to  the  resistance  of  the  conductors  and  which  reappears 
in  the  form  of  heat.  If  this  loss  is  not  kept  within  reasonable 
limits,  the  wires  will  become  very  hot  and  destroy  the  in- 
sulation or  ignite  surrounding  inflammable  material.  The 
above  loss  and  hazard  is  generally  guarded  against  by  insur- 
ance companies  and  inspection  boards  by  designation  of  the 
current  in  amperes  which  certain  wires  may  be  allowed  to 
carry. 

Table  No.  1  gives  the  currents  which  the  National  Board 
of  Fire  Underwriters  has  decided  to  consider  safe  and  which 


ELECTRICAL  TRANSMISSION  37 

should  be  closely  followed,  and  on  no  account  should  wires 
smaller  than  those  indicated  be  used.  There  is  no  harm  and 
no  objection  to  using  wires  larger  than  indicated,  but  neither 
is  there  much  gained  unless  the  run  be  a  long  one  as  we  shall 
see  further  on. 

The  table  of  carrying  capacities  shows  a  great  discrepancy 
between  the  relative  cross-section  of  large  and  small  wires 
and  the  currents  they  are  allowed  to  carry;  thus  a  No.  0000 
wire  has  a  cross-section  about  eight  times  as  great  as  that  of 
No.  6,  yet  is  allowed  to  carry  less  than  five  times  as  much. 

This  discrepancy  arises  from  the  different  rate  of  heat 
radiation.  The  radiating  surface  or  circumference  of  a  small 
circle  or  wire  is  relatively  to  its  cross-section  much  greater 
than  that  of  a  large  circle,  and  other  things  being  equal  the 
ratio  existing  between  the  heat  given  to  a  body  and  its  radiat- 
ing surface  determine  its  temperature. 

We  have  seen  before  that  the  power  (either  for  lights  or 
motors)  consists  of  two  factors;  current  and  pressure,  ex- 
pressed respectively  as  amperes  and  volts.  We  have  also  seen 
that  the  power  (watts)  equals  the  product  of  these  two; 
hence  it  follows,  that  as  we  increase  either  one,  we  may  de- 
crease the  other,  or  conversely,  as  one  is  decreased  the  other 
must  be  increased  in  order  to  deliver  a  given  amount  of 
power.  We  further  know  that  it  is  the  current  alone  which 
heats  the  wires  and  that  accordingly  as  our  currents  are  large 
or  small,  the  wires  used  to  transmit  them  must  be  large  or 
small.  It  is  obvious,  therefore,  that  we  can  save  much  on 
copper  by  using  higher  voltages,  since,  if  we  double  the 
voltage,  we  shall  need  only  one-half  as  much  current  and  can, 
therefore,  use  a  much  smaller  wire.  As  an  example:  Sup- 
pose we  have  power  to  transmit  which  at  110  volts  requires 
90  amperes.  This  requires  a  No.  2  wire  containing  66,370 
circular  mils.  Now,  if  we  double  the  voltage,  we  shall  need 
only  45  amperes;  this  much  we  are  allowed  to  transmit  over 


38  MODERN   ELECTRICAL  CONSTRUCTION. 

a  No.  6  wire  which  has  only  26,250  circular  mils.  We  must 
not,  however,  increase  our  voltage  without  due  precaution  and 
consideration,  for  high  voltage  is  dangerous  to  life  and  in- 
creases the  fire  hazard.  It  also  increases  the  liability  to 
leakage  and  requires  better  and  more  expensive  insulation 
which  in  a  small  measure  offsets  the  other  advantages.  The 
usual  voltage  employed  at  present  varies  from  110  to  220 
volts  for  indoor  lighting  and  power;  500  to  650  volts  for 
street  railway  work  and  from  2  to  20,000  volts  for  long 
distance  transmission.  The  higher  voltages  mentioned  are 
seldom  brought  into  buildings,  and  are  nearly  always  used 
with  some  transforming  device  which  reduces  the  pressure  to 
110  or  220  volts  for  indoor  lighting  or  power. 

The  flow  of  current  through  a  given  lamp,  motor,  or  re- 
sistance determines  the  light,  power  or  heat  obtainable  from 
such  device.  We  know  that  the  flow  of  current  in  turn 
(other  things  being  equal)  varies  as  the  E.  M.  F.  maintained 
at  the  terminals  of  any  of  these  devices.  Consequently  in 
order  to  obtain  a  steady  flow  of  current  it  is  necessary  to 
provide  a  steady  E.  M.  F. 

The  loss  of  E.  M.  F.  in  any  wire  is  equal  to  the  current 
flowing  in  that  wire  multiplied  by  the  resistance  of  the  wire. 
Since  it  is  impossible  to  obtain  wires  without  resistance,  it 
is  also  impossible  to  establish  a  circuit  without  loss  and 
wherever  electricity  is  used  some  loss  must  be  reckoned  with. 
We  may  make  this  loss  as  large  or  as  small  as  we  'desire. 
Where  the  cost  of  fuel  is  high,  it  is  important  to  keep  this 
loss  quite  small,  using  for  that  purpose  larger  wires.  On  the 
other  hand  where  there  is  an  abundance  of  cheap  fuel,  or, 
where,  for  instance,  water  power  is  used,  it  will  be  more 
economical  to  waste  five  or  ten  per  cent  of  the  electrical 
energy  than  to  spend  the  money  needed  to  provide  the  copper 
necessary  to  reduce  the  waste  to  one  or  two  per  cent. 

In  this  connection,  however,  it  must  not  be  overlooked  that 


ELECTRICAL  TRANSMISSION  39 

the  quality  of  the  service  depends  to  a  great  extent  upon  the 
loss  allowed  and  here  the  nature  of  the  business  supplied  must 
be  taken  into  consideration.  In  yards,  warehouses,  barns, 
etc.,  a  variation  of  five  or  ten  per  cent  in  candle  power  may 
not  matter  much,  but  in  residences  or  offices  it  is  very 
annoying. 

The  loss  in  voltage  depends,  as  we  have  already  seen, 
upon  the  current  used,  and  the  resistance  of  the  wire  em- 
ployed. If  the  current  is  decided  upon,  we  can  reduce  the  loss 
only  by  reducing  the  resistance;  the  resistance  can  be  re- 
duced only  by  increasing  the  size  of  wire  used.  If  we  double 
the  cross-section  of  the  wire,  we  decrease  the  resistance  one- 
half  and  consequently  reduce  the  loss  or  variation  in  volt- 
age one-half.  Thus  it  will  be  seen  that  as  we  attempt  to 
reduce  the  loss  in  voltage  to  a  minimum  we  shall  require 
very  large  wires  and  thus  greatly  increase  the  cost  of  our 
installation. 

For  instance,  if  a  line  be  in  operation  with  a  loss  -»f 
twenty  per  cent,  by  doubling  the  amount  of  copper,  we  reduce 
the  loss  to  ten  per  cent.  In  order  to  reduce  our  loss  to  five 
per  cent,  we  must  again  double  the  amount  of  copper;  and 
to  reduce  the  loss  still  more,  say  to  2l/2  per  cent,  a  wire 
of  double  the  cross-section  of  the  last  must  be  used.  If  the 
cost  of  copper  in  the  original  installation  utilizing  eighty  per 
cent  of  the  energy  be  taken  as  1,  then  the  cost  of  copper  to 
utilize  ninety  per  cent  will  be  2;  of  ninety-five  per  cent,  4; 
and  of  ninety-seven  and  one-half  per  cent,  8;  and  no  amount 
of  copper  will  eVer  be  able  to  save  the  full  100  per  cent. 
We  must  not  overlook,  however,  that  although  a  reduction  of 
loss  from  four  to  two  per  cent  requires  us  to  double  the 
amount  of  copper,  it  does  not  necessarily  double  the  cost  of 
our  installation,  for  in  many  cases  it  adds  but  a  small  per- 
centage to  the  total  cost.  For  instance,  if  it  were  decided  to 
use  No.  12  instead  of  No.  14  wire  in  moulding  or  insulator 


40  MODERN   ELECTRICAL  CONSTRUCTION. 

work,- the  cost  of  labor  would  not  be  appreciably  affected 
thereby;  similarity  in  connection  with  a  pole  line,  the  dif- 
ference in  total  cost  occasioned  by  the  use  of  say  No.  6 
instead  of  No.  10  wire  would  be  small. 


Calculation  of  Wires. 

In  electrical  calculations  so  far  as  they  relate  to  wiring, 
the  circular  mil  plays  an  important  part,  and  it  becomes 
necessary  to  thoroughly  understand  its  meaning.  The  mil 
is  the  1/1000  part  of  an  inch,  consequently  one  square  inch 
contains  1,000x1,000  equals  1,000,000  square  mils.  If  all  elec- 
trical conductors  were  made  in  rectangular  form,  we  should 
be  able  to  get  along  nicely  by  the  use  of  the  square  mil,  but, 
since  they  are  nearly  all  in  circular  form,  the  use  of  the  square 
mil  as  a  unit  would  necessitate  otherwise  unnecessary  figures. 
The  circular  mil  means  the  cross-section  of  a  circle  one  mil 
in  diameter,  whereas  the  square  mil  means  a  square  each 
side  of  which  is  equal  to  one  mil  in  length.  Square  mils, 
can,  therefore,  be  transformed  into  circular  mils  by  dividing 
by  .7854,  and  circular  mils  into  square  mils  by  multiplying 
by  .7854,  since  it  is  well  known  that  a  circle  which  can  be 
inscribed  within  a  square  bears  to  that  square  the  ratio  of 
.7854  to  1. 

To  illustrate:  Using  square  mils  if  we  wish  to  determine 
the  cross-section  of  a  wire  having  a  diameter  of  50  mils,  we 
must  first  square  the  diameter  and  then  multiply  by  .7854; 
50  X  50  X  .7854,  or  1963.5,  which  is  the  cross  section  of  the 
wire  expressed  in  square  mils.  To  express  the  cross-section 
in  circular  mils,  we  have  but  to  square  the  diameter,  or  50  X 
50  =  2500  circular  mils.  The  2500  circular  mils  are  exactly 
equal  to  the  1963.5  square  mils.  The  adoption  of  the  circular 
mil  simply  eliminates  the  figure  .7854  from  the  calculations. 

The  resistance  of  a  copper  wire  having  a  cross-section  of 


CALCULATION   OF   WIRES  *1 

one  mil  and  a  length  of  one  foot  is  from  10.7  to  10.8  ohms, 
the  variation  being  due  to  the  temperature  of  the  wire.  10.8 
ohms  is  the  resistance  usually  taken.  This  resistance  in- 
creases directly  as  the  length  and  decreases  as  the  cross-sec- 
tion increases.  The  resistance  of  any  copper  wire  can,  there- 
fore, be  found  by  multiplying  its  length  by  10.8  and  dividing 
by  the  number  of  circular  mils  it  contains.  Expressed  in 
L  X  10.8 

formula  this  becomes  R= where  L  stands  for  the 

C.  M. 

total  length  of  wire  in  feet,  and  C.  M.  for  the  cross-section 
in  circular  mils,  and  R  for  the  resistance  in  ohms.  In 
order  to  find  the  loss  in  volts,  we  must  multiply  the  resistance 
by  the  current  used.  Representing  this  current  by  I,  the 

I  X  L  X  10.8 

formula  becomes  —  —  =  V;  V  being  the  volts  lost. 

C.  M. 

It  is,  however,  seldom  necessary  to  find  how  many  volts  would 
be  lost  with  a  certain  wire  and  current,  but  rather  to  find  how 
many  circular  mils  are  necessary  in  a  wire  so  that  the  volts  lost 
may  not  exceed  a  certain  percentage.  In  order  to  determine  this, 
we  transpose  V  and  C.  M.  and  the  formula  now  becomes 
I  X  L  X  10.8 

=  C.  M.     This  is  the  final  formula  and  gives 

V 

directly  the  number  of  circular  mils  a  wire  must  have  so  that 
the  loss  with  this  current  and  length  of  wire  shall  not  exceed 
the  limits  set  by  V. 

As  an  example,  we  have  a  current  of  20  amperes  to  trans- 
mit a  distance  of  200  feet  and  the  bss  shall  not  exceed 
two  per  cent;  voltage  110.  This  requires  400  feet  of  wire 
(two  wires  200  feet  long)  and  two  per  cent  of  110  is  2.2.  We 
therefore  have  20  X  400  X  10.8  divided  by  2.2,  which  gives 
us  39,270  circular  mils,  which  we  see  by  table  I  is  a  little  less 
than  a  No.  4  wire. 


42  MODERN   ELECTRICAL  CONSTRUCTION. 

The  above  formula  will  answer  for  all  2-wire  \vork> 
whether  it  be  lights  or  power. 

It  is  simply  necessary  to  find  the  current  required  with 
whatever  devices  are  to  be  used. 

These  calculations  are  not  often  made  in  actual  practice. 
It  is  much  easier  to  refer  to  tables  such  as  II,  III,  IV,  V,  VI, 
given  at  the  end  of  this  volume,  by  which  the  proper  size 
of  wire  can  be  determined  at  a  glance  almost. 

In  connection  with  3-wire  systems  using  two  lamps  in 
series,  we  need  to  calculate  the  two  outside  wires  only,  the 
neutral  wire  should  then  be  taken  of  the  same  size.  We  must 
however  assume  double  the  voltage  existing  on  either  side 
of  the  neutral;  that  is  to  say,  a  2-wire  system  using  110  volts 
would  be  figured  at  110  volts,  while  a  3-wire  system,  using 
110  volt  lamps  on  each  side  of  the  neutral  wire  would  be 
figured  at  220  volts. 

It  must  also  be  noted  that  with  3-wire  systems  the  cur- 
rent required  is  only  l/z  of  that  required  with  2-wire  sys- 
tems. Ordinarily  we  have  two  lamps  in  series  and  the  same 
current  passes  through  both.  Applying  this  to  our  formula 
we  see  that  with  the  3-wire  system  the  current  I  is  only  half 
as  great  as  with  2-wire  systems  and  (the  percentage  of  loss 
in  both  cases  being  the  same)  V,  which  stands  for  the  volts 
to  be  lost,  becomes  twice  as  great.  Owing  to  these  two  fac- 
tors, the  wire  for  3-wire  systems  need  have  only  %  as  many 
circular  mils  as  that  of  a  2-wire  system  with  the  same  per- 
centage of  loss.  To  this  must  be  added  the  neutral  wire  so 
that  the  total  cost  of  wire  must  be  Yt,  of  that  for  the  2-wire 
systems. 

The  amount  of  copper  required  in  power  transmission  for 
a  given  percentage  of  loss  varies  as  the  square  of  the  voltage 
employed.  By  doubling  the  voltage  we  can  transmit  power 
with  the  same  loss  four  times  as  far;  or,  if  we  do  not  change 
distance  or  wire,  we  shall  have  only  one-fourth  of  the  loss 


CALCULATION   OF   WIRES  43 

we  had  before.  A  practical  idea  of  the  laws  governing  the 
distribution  of  circuits  and  the  losses  in  voltage  and  wire 
which  are  unavoidable  may  be  gained  from  Figure  20. 

Figure  20  shows  96  incandescent  lights  arranged  on  one 
floor  and  placed  10  feet  apart  each  way.  With  all  cutouts 
placed  at  A  and  circuits  arranged  as  in  No.  1,  2,080  feet  of 
branch  wiring  for  the  eight  circuits  of  12  lights  each,  will  be 
required.  If  the  cutouts  be  placed  in  the  center,  B,  the  same 
length  of  wire  will  be  necessary.  We  have  in  this  case  merely 
transferred  the  cross  wires  from  one  end  of  the  hall  to  the 
center.  If  we  arrange  two  sets  of  cutouts  as  at  C  and  D 
and  run  circuits  as  3  and  4  the  total  amount  of  wire  necessary 
will  be  only  1,920  feet.  By  this  arrangement  we  avoid  the 
necessity  of  crossing  the  space  indicated  by  dotted  lines  at 
the  right,  opposite  B. 

If  we  run  the  circuits  on  the  plan  of  No.  2,  the  least  amount 
of  wire  for  the  eight  circuits  will  be  2,560  ft.  Such  wir- 
ing would  require  extra  wires  feeding  the  various  groups. 
Should  we  run  a  set  of  mains  along  ACBD,  and  make  12 
circuits  of  the  installation  by  placing  one  cutout  for  each 
eight  lights,  the  amount  of  wire  required  will  be  1,680  feet. 
If  we  run  a  set  of  mains  through  B  as  shown  by  dotted  lines 
using  12  lights  per  circuit,  1,760  feet  of  wire  will  be  re- 
quired. If  we  now  double  the  number  of  lights  in  the  same 
space  or  limit  the  number  per  circuit  to  six,  we  shall  require 
3,200  feet  of  wire  to  feed  them  all  from  A,  but  only  2,400  to 
feed  them  from  B ;  to  feed  them  all  from  the  two  centers  C 
and  D  will  also  require  2,400  feet. 

The  most  economical  location  of  cutout  centers  will,  with 
even  distribution  of  light,  and  in  regard  to  branch  wiring 
only,  be  such  that  it  is  unnecessary  to  run  circuits  like  No.  2; 
in  other  words,  not  more  than  the  number  of  lights  allowed  on 
one  circuit  should  lead  away  from  it  in  one  direction. 

Suppose,  for  instance,  the  number  of  lights  be  increased 


44 


MODERN   ELECTRICAL  CONSTRUCTION. 


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CALCULATION   OF  WIRES  45 

by  one-half  or  (which  amounts  to  the  same  thing  in  wire), 
the  number  of  lights  per  circuit  be  limited  to  eight.  If  we 
run  all  branch  circuits  from  A,  we  shall  need  a  total  of  2,760 
feet.  It  will  require  just  as  much  wire  to  run  the  64  lights 
below  X  as  was  required  to  run  the  whole  96  before ;  viz. : 
2,080  feet ;  to  this  must  be  added  the  wire  necessary  to  run  the 
four  circuits  above  which  is  680  feet.  By  extending  our 
mains  to  the  point  X,  we  car  save  eight  runs  of  wire  each 
equal  in  length  to  the  distance  between  A  and  X.  X  is  the 
point  of  extreme  economy  as  regards  branch  wires  and  nothing 
can  be  gained  in  this  respect  by  extending  the  mains  any 
further  unless  several  cutout  centers  are  decided  upon  as 
before  explained.  Whether  it  be  more  economical  to  extend 
the  mains  to  X,  or  run  branch  circuits  from  A,  depends  upon 
the  relative  cost,  in  this  instance,  of  30  feet  of  mains  and 
480  feet  of  branch  wires. 

With  an  uneven  distribution  of  lights  as  indicated  by  the 
black  circles,  each  of  which  may  be  taken  as  an  arc  lamp  or 
cluster  of  incandescent  lamps,  the  most  economical  location 
of  cutouts  will  be  at  Z.  To  move  them  farther  to  the  right 
would  shorten  the  wires  of  five  circuits  and  lengthen  them  on 
eight ;  to  move  either  up  or  down  in  the  group  of  eight  would 
also  lenghten  more  wires  than  it  would  shorten. 

In  laying  out  circuits  for  electric  lights,  however,  we 
must  not  take  into  consideration  the  cost  of  wire  only.  In 
many  cases  the  loss  in  voltage  is  of  far  greater  importance, 
not  only  because  it  means  a  steady  waste  of  power,  but  also 
because  of  unsatisfactory  illumination,  lamps  in  different 
parts  of  a  circuit  not  being  of  the  same  candle  power,  or 
the  light  in  one  place  varying  greatly  when  lights  in  another 
place  are  turned  on  or  off. 

Some  idea  of  the  variation  in  voltage  in  different  parts 
of  differently  arranged  circuits  can  be  obtained  from  Figure  20. 
The  length  of  wire  in  circuit  1  is  35  feet  to  the  first  lamp  and 


46  MODERN   ELECTRICAL  CONSTRUCTION. 

10  feet  from  this  to  the  next,  etc.  The  voltage  at  the  cut- 
out A  is  110  and  at  each  lamp  is  given  the  actual  voltage 
existing  at  that  point  with  all  lamps  burning.  The  wire  of 
the  circuit  is  No.  14  and  with  55  watt  lamps,  the  loss  to  the 
last  lamp  over  a  run  of  145  feet  is  a  trifle  over  two  and  one- 
half  per  cent  when  all  lamps  are  burning. 

Circuit  No.  2  is  figured  as  of  the  same  length  as  No.  1, 
and  supplies  the  same  number  of  lamps,  but  ct  a  much  greater 
loss,  slightly  over  four  per  cent  to  the  last  lamp.  Circuits  3 
and  4  feeding  from  C  contain  equal  lengths  of  wire,  but 
there  is  quite  a  difference  in  loss;  in  3  only  .75  of  one  volt, 
while  in  4  it  is  a  little  over  two  volts.  From  study  of  Figure 
20  we  may  learn  that  the  arrangement  of  circuit  1  is  fairly 
satisfactory  especially  if  the  nature  of  the  work  done  under 
it  is  such  that  only  part  of  the  lamps  are  used  at  the  same 
time.  Circuit  No.  2  is  bad  if  all  lights  are  used  at  once,  and 
it  should  be  wired  with  No.  10  or  12  wire.  Whenever  the  loca- 
tion of  lights  is  such  as  to  allow  a  circuit  like  No.  3  to  be  run, 
the  loss  can  be  kept  very  low  with  a  minimum  of  wire.  In 
general  the  more  cutout  centers  there  are  established  in  propor- 
tion to  the  number  of  lights,  if  mains  are  properly  arranged, 
the  less  will  be  the  loss  in  pressure  and  the  more  satisfactory 
the  service. 


NOTICE.— DO  NOT  FAIL  TO  SEE  WHETHER  ANY 
RULE  OR  ORDINANCE  OF  YOUR  CITY  CONFLICTS 
WITH  THESE  RULES. 


CLASS  A. 
STATIONS  AND  DYNAMO  ROOMS. 

Includes  Central  Stations,  Dynamo,  Motor  and  Storage- 
Battery  Rooms,  Transformer  Substations,  Etc. 

1.    Generators. 

a.  Must  be  located  in  a  dry  place. 

Perfect  insulation  in  electrical  apparatus  requires  that  the 
material  used  for  insulation  be  kept  dry.  While  in  the  con- 
struction of  generators  the  greatest  care  is  taken,  so  that  all 
current  carrying  parts  are  well  insulated,  still,  if  moisture  is 
allowed  to  settle  on  the  insulation,  trouble  is  almost  sure  to 
occur.  For  this  reason  a  generator  should  never  be  installed 
where  it  will  be  exposed  to  steam  or  damp  air,  or  in  any  place, 
where  through  accident,  water  may  be  thrown  against  it. 

b.  Must  never  be  placed  in  a  room  where  any  hazardous 
process  is  carried  on,  nor  in  places  where  they  would  be  ex- 
posed to  inflammable  gases  or  flyings  of  combustible  materials. 

In  even  the  best  constructed  dynamos  there  is  always  more 
or  less  sparking  at  the  brushes  and  small  pieces  of  hot  carbon 
are  sometimes  thrown  off.  As  a  general  rule  in  buildings 
where  there  is  considerable  dust,  such  as  in  wood-working 
plants,  grain  elevators  and  the  like,  the  dynamo  is  located  in 
the  engine  room,  which  is  generally  isolated  from  the  dusty 
part  of  the  building. 

c.  Must  be  thoroughly  insulated  from  the  ground  wherever 
feasible.     Wooden   base-frames   used    for   this   purpose,   and 


48 


MODERN   ELECTRICAL  CONSTRUCTION. 


wooden  floors  which  are  depended  upon  for  insulation  where, 
for  any  reason,  it  is  necessary  to  omit  the  base-frames,  must 
be  kept  filled  to  prevent  absorption  of  moisture,  and  must  be 
kept  clean  and  dry. 

Where  frame  insulation  is  impracticable,  the  Inspection 
Department  having  jurisdiction  may,  in  writing,  permit  its 
omission,  in  which  case  the  frame  must  be  permanently  and 
effectively  grounded. 

A  high-potential  machine,  which  on  account  of  great  weight 
or  for  other  reasons,  cannot  have  its  frame  insulated  from  the 
ground,  should  be  surrounded  with  an  insulated  platform. 
This  may  be  made  of  wood,  mounted  on  insulating  supports, 
and  so  arranged  that  a  man  must  always  stand  upon  it  in  order 
to  touch  any  part  of  the  machine. 

In  case  of  a  machine  having  an  insulated  frame,  if  there  is 
trouble  from  static  electricity  due  to  belt  friction,  it  should 
be  overcome  by  placing  near  the  belt  a  metallic  comb  connected 
with  the  earth,  or  by  grounding  the  frame  through  a  very 
high  resistance  cf  not  less  than  300,000  ohms. 

The  smaller  generators  are  usually  insulated  on  wooden 
base  frames.  A  base  frame  suitable  for  this  work  is  shown  in 


Figure  21 


Figure  22 


Figure  21.  Almost  any  kind  of  wood,  well  varnished,  is  very 
good  for  this  purpose.  The  base  frame  is  screwed  to  the  floor  or 
foundation  and  the  slide  rail  (which  is  used  where  the  dy- 
namo is  belted  to  the  engine  to  allow  the  tightening  and  slack- 


GENERATORS  49 

ening  of  the  belt)  is  independently  attached  to  it,  that  is, 
the  same  bolt  must  not  be  used  to  hold  the  slide  rail  to  the 
base  frame  and  the  base  frame  to  the  floor,  as  this  would  be 
liable  to  ground  the  frame.  The  direct  connected  machines 
(dynamo  and  engine  on  same  bed  plate)  are  often  insulated 
by  the  use  of  mica  washers  and  bushings  surrounding  the 
bolts  which  fasten  the  dynamo  to  the  bed  plate  and  by  using 
an  insulated  flange  coupling  between  the  shaft  of  the  dynamo 
and  that  of  the  engine.  Figure  22  shows  a  section  of  a  flange 
coupling  insulated  in  this  way,  the  heavily  shaded  parts  rep- 
resenting the  insulating  material. 

The  larger  machines,  which  on  account  of  their  weight 
cannot  be  insulated,  must  be  permanently  and  effectually 
grounded.  Where  the  engine  and  dynamo  are  direct  con- 
nected a  very  good  ground  is  obtained  through  the  engine  con- 
nections. Where  belts  arc  used  a  good  ground  can  be  ob- 
tained by  fastening  a  copper  wire  under  one  of  the  bolts  on  the 
dynamo  and  connecting  the  other  end  of  the  wire  to  available 


Figure  23 

water  pipes.  In  the  case  of  high  tension  machines,  especially 
series  arc,  the  machine  should  always  be  surrounded  by  an 
insulated  platform  so  arranged  that  a  man  must  stand  on  it  in 
order  to  touch  any  part  of  the  machine  either  live  parts  or 


SO  MODERN   ELECTRICAL  CONSTRUCTION. 

frame  and  in  handling  such  a  machine  only  one  hand  at  a  time 
should  be  used.  A  hardwood  platform  mounted  on  insulators 
will  serve  very  well  for  this  purpose  or  suitable  platforms  may 
be  obtained  from  dealers  in  electrical  supplies. 

Figure  23  shows  a  metallic  comb  such  as  is  occasionally 
used  to  overcome  the  static  electricity  due  to  the  friction  of 
the  belt.  A  strip  of  metal,  one  end  of  which  is  cut  with  a 
number  of  projecting  points,  is  suspended  crosswise  a  short 
distance  above  the  belt.  A  wire  connects  this  plate  to  any 
suitable  ground. 

A  resistance  for  grounding  the  generator  frame  in  accord- 
ance with  this  rule  is  constructed  of  ground  glass  equipped 
with  two  metal  terminals  separated  a  short  distance  and  con- 
nected by  means  of  a  lead  pencil  mark.  One  terminal  is  con- 
nected to  the  frame  of  the  machine  and  the  other  to  the  ground. 

d.  Every  constant-potential  generator  must  be  protected 
from  excessive  current  by  a  safety  fuse,  or  equivalent  device 
of  approved  design  in  each  lead  wire. 

These  devices  should  be  placed  on  the  machine  or  as  near 
it  as  possible. 

Where  the  needs  of  the  service  make  these  devices  imprac- 
ticable, the  Inspection  Department  having  jurisdiction  may,  in 
writing,  modify  the  requirements. 

The  fuses  required  by  this  rule  are  often  mounted  on  the 
dynamo,  but  the  general  practice  at  the  present  time  is  to 
mount  all  fuses  on  the  switchboard.  A  fuse  should  be  placed 
in  each  lead ;  that  is,  each  of  the  main  wires  from  the  dynamo 
should  be  protected  by  a  fuse.  A  fuse  should  never  be  placed 
in  the  field  circuit  wire.  Where  two  or  more  dynamos  are 
run  in  parallel  the  equalizer  connection  (a  wire  connecting  all 
the  armature  terminals  from  which  the  series  fields  are  taken 
and  which  tends  to  equalize  the  load  between  the  various  ma- 
chines) is  sometimes  carried  through  a  3-pole  switch  on  the 
switchboard  and  is  often  fused.  It  is  immaterial  whether  this 
equalizer  is  fused  or  not,  as  fusing  it  adds  no  protection.  If  it 


GENERATORS  51 

is  fused  the  fuse  should  be  at  least  the  same  size  as  used  in 
the  leads. 

Circuit  breakers  are  very  often  used  for  the  protection  in 
the  dynamo  leads.  They  are  generally  mounted  on  the  switch- 
board and  connected  in  the  circuit  ahead  of  the  main  switch. 
As  a  general  rule  circuit  breakers  are  not  approved  unless 
fuses  are  also  installed  in  the  circuit.  The  circuit-breaker  as 
at  present  constructed  is  in  nearly  all  cases  a  much  more 
efficient  and  reliable  device  than  the  fuse,  and  its  use  is  to  be 
recommended.  Single-pole  circuit  breakers  are  approved  if  fuses 
are  also  used.  As  to  the  relative  currents  at  which  the  fuse 
and  circuit  breaker  should  be  set  to  operate,  authorities  differ. 
Some  advise  both  to  be  set  to  operate  at  the  same  current 
strength,  so  that  the  fuse,  which  takes  a  longer  time  to  operate, 
will  blow  only  in  case  the  circuit  breaker  fails.  Another  recom- 
mends the  fuses  to  be  of  such  capacity  as  to  carry  any  load 
which  will  be  required  of  them  and  to  set  the  circuit  breaker 
a  little  higher  than  the  fuses,  so  that  the  fuses  will  operate 
on  overload  and  the  circuit  breaker  on  short  circuit. 

The  practice  of  setting  the  fuses  at  about  twenty-five  per 
cent,  above  the  circuit  breaker  seems  to  be  preferred,  for  it 
occasionally  happens  when  both  are  set  to  operate  at  the  same 
current,  the  fuse  alone  will  "blow,"  due  to  the  excessive  heat 
produced  in  the  fuse  at  full  load. 

Cases  are  sometimes  found  where  the  cessation  of  current 
due  to  the  blowing  of  a  fuse  could  cause  more  damage  than 
would  result  from  an  overload,  as,  for  instance,  where  the 
dynamo  operates  some  safety  device.  In  cases  of  this  kind  the 
Inspection  Department  having  jurisdiction  may  modify  the 
requirements. 

e.  Must  each  be  provided  with  a  waterproof  cover. 

f.  Must  each  be  provided  with  a  name-plate,  giving  the 
maker's  name,  the  capacity  in  volts  and  amperes,  and  the  nor- 
mal speed  in  revolutions  per  minute. 


52  MODERN   ELECTRICAL  CONSTRUCTION. 

2.    Conductors. 

From  generators  to  switchboards,  rheostats  or  other  instru- 
ments, and  thence  to  outside  lines. 

a.  Must  be  in  plain  sight  or  readily  accessible. 

b.  Must  have  an  approved  insulating  covering  as  called  for 
by  rules  in  Class  "C"  for  similar  work,  except  that  in  central 
stations,  on  exposed  circuits,  the  wire  which  is  used  must  have 
a  heavy  braided,  non-combustible  outer  covering. 

Bus  bars  may  be  made  of  bare  metal. 

Rubber  and  "weatherproof"  insulations  ignite  easily  and 
burn  freely.  Where  a  number  of  wires  are  brought  close  to- 
gether, as  is  generally  the  case  in  dynamo  rooms,  especially 
about  the  switchboard,  it  is  therefore  necessary  to  surround 
this  inflammable  material  with  a  tight,  non-combustible  outer 
cover.  If  this  is  not  done,  a  fire  once  started  at  this  point 
would  spread  rapidly  along  the  wires,  producing  intense  heat 
and  a  dense  smoke.  Where  the  wires  have  such  a  covering 
and  are  well  insulated  and  supported,  using  only  non-com- 
bustible materials,  it  is  believed  that  no  appreciable  fire 
hazard  exists,  even  with  a  large  group  of  wires. 

c.  Must  be  kept  so  rigidly  in  place  that  they  cannot  come 
in  contact. 

d.  Must  in  all  other  respects  be  installed  with  the  same 
precautions  as  required  by  rules  in  Class  "C"  for  wires  carry- 
ing a  current  of  the  same  volume  and  potential. 

In  wiring  switchboards,  the  ground  detector,  volt  meter 
and  pilot  lights  must  be  connected  to  a  circuit  of  not  less  than 
No.  14  B.  &  S.  gage  wire  that  is  protected  by  a  standard  fuse 
block;  this  circuit  is  not  to  carry  over  660  watts. 

A  number  of  different  methods  are  used  for  running  wires 
in  dynamo  rooms.  Where  the  dyanmo  is  located  in  a  room 
with  a  low  ceiling,  or  where  it  is  not  desirable  to  run  the 
wires  open,  metal  conduits  may  be  imbedded  in  the  floor  and 
the  wires  run  in  them.  If  the  engine  room  is  located  in  the 
basement  or  in  any  place  where  water  or  moisture  is  liable 
to  gather  in  the  conduits  the  wires  should  be  lead  covered. 
At  outlets  the  conduits  should  be  carried  some  distance  above 
the  floor  level  and  close  to  the  frame  of  the  machine,  where 
they  will  be  protected  from  mechanical  injury.  If  the  space 
under  the  machine  will  allow  it,  the  conduit  should  be  ended 


SWITCHBOARDS  S3 

there  where  it  will  be  protected  by  the  base  frame.  Where 
lead  covered  wires  are  used,  the  lead  should  be  cut  back  some 
distance  from  the  exposed  part  of  the  wire  and  the  end  of  the 
lead  should  be  well  taped  and  compounded  so  that  no 
moisture  can  creep  in  between  the  lead  and  the  insulation. 

In  place  of  the  metal  conduits  tile  ducts  can  be  used ;  or, 
if  the  floor  is  of  cement,  a  channel  may  be  left  in  the  floor 
and  the  wires  run  in  it.  A  removable  iron  cover  should  be 
provided. 

The  wires  may  be  run  open  on  knobs  or  cleats  as  described 
in  Class  C.  Where  there  are  many  wires,  cable  racks,  con- 
structed of  wood  or  preferably  iron,  having  cleats  bolted  to 
them,  may  be  used.  As  a  general  rule  moulding  should  not 
be  used  for  this  class  of  work.  Especially  in  central  stations 
the  generators  are  often  called  upon  for  a  very  heavy  overload 
and  should  the  wires  become  overheated  a  fire  is  much  more 
apt  to  result  than  if  the  mains  were  run  open  where  any 
trouble  could  be  immediately  noticed. 

3.    Switchboards. 

a.  Must  be   so  placed   as  to   reduce   to   a   minimum   the 
danger  of  communicating  fire  to  adjacent  combustible  material. 

Special  attention  is  called  to  the  fact  that  switchboards 
should  not  be  built  down  to  the  floor,  nor  up  to  the  ceiling. 
A  space  of  at  least  10  or  12  inches  should  be  left  between  the 
floor  and  the  board,  and  3  feet,  If  possible,  between  the  ceiling 
and  the  board,  in  order  to  prevent  fire  from  communicating 
from  the  switchboard  to  the  floor  or  ceiling,  and  also  to  pre- 
vent the  forming  of  a  partially  concealed  space  very  liable  to 
be  used  for  storage  of  rubbish  and  oily  waste. 

b.  Must  be  made  of  non-combustible  material  or  of  hard- 
wood in  skeleton  form,  filled  to  prevent  absorption  of  moisture. 

If  wood  Is  used  all  wires  and  all  current-carrying1  parts  of 
the  apparatus  on  the  switchboard  must  be  separated  therefrom 
by  non-combustible,  non-absorptive  insulating  material. 

c.  Must  be  accessible  from  all  sides  when  the  connections 
are  on  the  back,  but  may  be  placed  against  a  brick  or  stone 
wall  when  the  wiring  is  entirely  on  the  face. 


54 


MODERN  ELECTRICAL  CONSTRUCTION. 


If  the  wiring  Is  on  the  back,  there  should  be  a  clear  space 
of  at  least  18  inches  between  the  wall  and  the  apparatus  on 
the  board,  and  even  if  the  wiring  is  entirely  on  the  face,  it  is 
much  better  to  have  the  board  set  out  from  the  wall.  The 
space  back  of  the  board  should  not  be  closed  in,  except  by 
grating  or  netting  either  at  the  sides,  top  or  bottom,  as  such 
an  enclosure  is  almost  sure  to  be  used  as  a  closet  for  clothing 
or  for  the  storage  of  oil  cans,  rubbish,  etc.  An  open  space  is 
much  more  likely  to  be  kept  clean,  and  is  more  convenient  for 
making  repairs,  examinations,  etc. 

d.  Must  be  kept  free  from  moisture. 

e.  On  switchboards  the  distances  between  bare  live  parts 


nl 


Figure  24 


of  opposite  polarity  must  be  made  as  great  as  practicable,  and 
must  not  be  less  than  those  given  for  tablet-boards  (see  No. 
oo  A). 

The  switchboard  may  be  located  in  any  suitable  place  in  the 


RESISTANCE  BOXES  55 

dynamo  room.  It  should  generally  be  placed  in  a  central 
position  as  close  as  possible,  without  inconvenience,  to  all 
machines  and  perfectly  accessible.  Do  not  locate  a  switchboard 
under  or  near  a  steam  or  water  pipe  or  too  close  to  windows, 
as  these  may  accidentally  be  the  means  of  wetting  the  board. 

The  material  generally  used  for  the  construction  of  switch- 
boards is  slate  or  marble,  free  from  metallic  veins.  If  metallic 
veins  are  not  guarded  against  they  may  cause  great  leakage  of 
current,  which  will  manifest  itself  in  heating  the  slate  or 
marble. 

The  switchboard  may  be  made  of  hardwood  in  skeleton 
form  (see  Figure  24),  but  in  this  case  all  switches,  cutouts, 
instruments,  etc.,  must  be  mounted  on  non-combustible,  non- 
absorptive  insulating  bases,  such  as  slate  or  marble  and  all 
wires  must  be  properly  bushed  where  they  pass  through  the 
woodwork  and  must  be  supported  on  cleats  or  knobs.  Wood 
base  instruments  are  not  approved. 

Marble  or  slate  boards  are  usually  set  in  angle  iron  frames 
and  are  much  safer  and  better  than  the  skeleton  board  shown. 
It  is  a  good  plan  to  have  the  iron  legs  rest  on  a  wooden  base, 
so  that  they  will  be  insulated  from  the  ground. 

Although  only  18  inches  clear  space  is  required  back  of 
the  board,  where  the  board  is  back  connected,  this  should  be 
increased  wherever  possible,  especially  in  the  case  of  large 
boards. 

4.    Resistance  Boxes  and  Equalizers. 

(For  construction  rules,  see  No.  60.) 

a.  Must  be  placed  on  a  switchboard  or,  if  not  thereon, 
at  a  distance  of  at  least  a  foot  from  combustible  material,  or 
separated  therefrom  by  a  non-inflammable,  non-absorptive, 
insulating  material  such  as  slate  or  marble. 

The  attachments  of  the  separating  material  to  its  support 
and  to  the  device  must  be  independent  of  each  other,  and  the 
separating  material  must  be  continuous  between  the  device  and 
the  support;  that  is,  the  use  of  porcelan  knobs  will  not  be 
accepted. 


56  MODERN   ELECTRICAL   CONSTRUCTION. 

Ordinarily  the  dynamo  field  rheostat  is  mounted  on  the 
back  of  the  board  if  the  board  is  back  connected,  a  small  hand 

wheel   being  provided   so  that  ___ 

the   rheostat  may  be  operated  [ 

from  the  front  of  the  board. 
If  the  switchboard  is  in  skele- 
ton form,  or  if  the  rheostat  is 
placed  on  a  wall,  it  should  be 
mounted  on  a  solid  piece  of 
slate  or  marble.  Separate 

screws  should  be  used  for  at-  rig  £5. 

taching  the  rheostat  to  the  slate 

or  marble  and  the  slate  or  marble  to  the  wall,  for,  if  the  same 
screws  were  used  for  this  purpose,  they  would  be  apt  to  ground 
the  rheostat  frame.  (See  Figure  25.) 

On  central  stations  where  current  is  furnished  over  a  large 
area,  there  is  on  some  of  the  circuits,  especially  the  long  ones, 
a  considerable  "drop,"  or  loss  of  potential.  In  order  to  keep 
the  voltage  at  the  point  of  supply  on  these  circuits  at  the 
proper  value,  the  voltage  at  the  station  must  be  raised.  This 
in  turn  causes  the  voltage  on  those  circuits  near  the  dynamo 
to  become  excessive.  Equalizers,  which  are  large  resistance 
boxes  generally  constructed  of  iron  wire  or  strips,  and  capable 
of  carrying  a  heavy  current,  are  connected  in  the  circuits  and 
adjusted  at  such  resistances  as  to  make  the  voltage  at  the 
various  points  of  supply  uniform.  They  are  generally  too 
heavy  to  mount  on  the  board,  but  should  be  raised  on  non- 
combustible,  non-absorptive,  insulating  supports  and  should 
be  separated  from  all  inflammable  material. 

b.  Where  protective  resistances  are  necessary  in  connec- 
tion with  automatic  rheostats,  incandescent  lamps  may  be 
used,  provided  that  they  do  not  carry  or  control  the  main 
current  or  constitute  the  regulating  resistance  of  the  device. 

When  so  used,  lamps  must  be  mounted  in  porcelain  recep- 


LIGHTNING   ARRESTORS  57 

tacles  upon  non-combustible  supports,  and  must  be  so  arranged 
that  the}'  cannot  have  impressed  upon  them  a  voltage  greater 
than  that  for  which  they  are  rated.  They  must  in  all  cases  be 
provided  with  a  name-plate,  which  shall  be  permanently  at- 
tached beside  the  porcelain  receptacle  or  receptacles  and 
stamped  with  the  candle-power  and  voltage  of  the  lamp  or 
lamps  to  be  used  in  each  receptacle. 

5.     Lightning  Arresters. 

(  For  construction  rules,  sec  No.  63.) 

a.  Must  be  attached  to  each  wire  of  every  overhead  cir- 
cuit connected  with  the  station. 

It  is  recommended  to  all  electric  light  and  power  companies 
that  arresters  be  connected  at  intervals  over  systems  in  such 
numbers  and  so  located  as  to  prevent  ordinary  discharges  en- 
tering (over  the  wires)  buildings  connected  to  the  lines. 

b.  Must  be  located  in  readily  accessible  places  away  from 
combustible  materials,  and  as  near  as  practicable  to  the  point 
where  the  wires  enter  the  building. 

Station  arresters  should  generally  be  placed  in  plain  sight 
on  the  switchboard. 

In  all  cases,  kinks,  coils  and  sharp  bends  in  the  wires  be- 
tween the  arresters  and  the  outdoor  lines  must  be  avoided  as 
far  as  possible. 

c.  Must  be  connected  with  a  thoroughly  good  and  perma- 
nent ground  connection  by  metallic  strips  or  wires  having  a 
conductivity  not  less  than  that  of  a  No.  6  B.  &  S.  gage  copper 
wire,  which  must  be  run  as  nearly  in  a  straight  line  as  possible 
from  the  arresters  to  the  ground  connection. 

Ground  wires  for  lightning  arresters  must  not  be  attached 
to  gas  pipes  within  the  buildings. 

It  Is  often  desirable  to  introduce  a  choke  coil  in  circuit 
between  the  arresters  and  the  dynamo.  In  no  case  should  t^.e 
ground  wires  from  the  lightning  arresters  be  put  into  ircn 
pipes,  as  these  would  tend  to  impede  the  discharge. 

A  lightning  discharge  is  simply  a  discharge  of  electricity  at 


58  MODERN  ELECTRICAL  CONSTRUCTION. 

very  high  potential.  While  the  insulation  of  the  ordinary  wire 
serves  very  well  for  the  voltages 
for  which  it  is  used  it  offers  very 
little  resistance  to  a  current  of 
such  high  potential,  and  providing 
the  discharge  can  reach  the  ground 
by  jumping  through  the  insula- 
tion, it  will  generally  take  that 
course  unless  some  easier  path  is 
offered  to  it.  A  lightning  arrester 
in  its  simplest  form  consists  of 
Fig.  26.  two  metal  plates  separated  by  a 

small  air  space  as  shown  in  Fig- 
ure 26.     One  of  the  plates  is  con- 
nected to  the  line  and  the  other  to  the  ground,  a  set  being  pro- 
vided for  each  line  wire  to  be  protected. 

The  air  space  between  the  metal  plates  offers  a  much  lower 
resistance  to  the  passage  of  such  a  sudden  current  as  a  dis- 
charge of  lightning  consists  of,  than  do  the  magnets  of  a 
dynamo,  for  instance,  or  highly  insulated  parts  of  the  line. 
The  current,  therefore,  jumps  the  air  space  and  passes  to 
ground.  When  the  current  jumps  this  air  space  it  produces 
an  arc  similar  to  that  seen  in  an  arc  lamp,  and  after  the  light- 
ning discharge  is  over  the  dynamo  current  is  very  likely  to 
maintain  this  arc  and  thus  cause  a  short  circuit  from  one 
lightning  arrester  through  the  ground  to  the  other.  Different 
methods  of  preventing  this  by  interrupting  the  arc  have  been 
devised. 

Figure  27  shows  the  T.  H.  lightning  arrester,  in  which 
the  arc  is  extinguished  by  a  magnetic  field  set  up  by  the  electro- 
magnet. In  the  Wurts  non-arcing  lightning  arrester  (Figure 
28)  the  discharge  takes  place  across  the  air  gaps  between  the 
cylinders ;  these  are  made  of  a  metal  which  will  not  arc. 

A  choke  coil  is  essentially  an  electro-magnet,  and  like  all 


TESTING  59 

magnets  offers  a  ve.ry  high  resistance  to  a  sudden  rise  in  cur- 
rent strength,  and  is,  therefore,  an  additional  protection  to 
other  magnets  in  the  circuit. 

6.    Care  and  Attendance. 

a.    A  competent  man  must  be  kept  on  duty  where  gen- 
erators are  operating. 


Figure  27 

b.  Oily  waste  must  be  kept  in  approved  metal  cans  and 
removed  daily. 

Approved  waste  cans  shall  be  made  of  metal,  with  legs 
raising  can  3  inches  from  the  floor  and  with  self-closing 
covers. 

7.    Testing  of  Insulation  Resistance. 

a.  All  circuits  except  such  as  are  permanently  grounded 
in  accordance  with  Rule  13  A  must  be  provided  with  reliable 
ground  detectors.  Detectors  which  indicate  continuously  and 


60 


MODERN   ELECTRICAL  CONSTRUCTION. 


give  an  instant  and  permanent  indication  of  a  ground  are 
preferable.  Ground  wires  from  detectors  must  not  be  at- 
tached to  gas  pipes  within  the  building. 

b.  Where  continuously  indicating  detectors  are  not  feasible 
the  circuits  should  be  tested  at  least  once  per  day,  and  prefer- 
ably oftener. 

c.  Data  obtanied  from  all  tests  must  be  preserved  for  ex- 


Figure  28 

animation  by  the  Inspection  Department  having  jurisdiction. 

These  rules  on  testing  to  be  applied  to  such  places  as  may 
be  designated  by  the  Inspection  Department  having  jurisdic- 
tion. 

The  exceptions  to  this  rule  are  3-wire  direct  current  sys- 
tems where  the  neutral  is  grounded  and  2  and  3-wire  alter- 
nating current  secondaries  where  the  neutral  or  one  side  is 
grounded. 


TESTING  61 

In  every  installation  of  electric  wiring  there  is  a  certain 
"leak"  of  current.  This  leak  is  partly  between  the  wires  and 
the  ground  and  between  the  wires  themselves.  The  amount  of 
leak  varies,  but  is  always  dependent  on  the  insulation  resist- 
ance. Where  a  small  amount  of  wire  is  well  installed  the  leak" 
should  be  very  small,  but  in  the  case  of  large  installations 
or  where  the  wiring  has  been  poorly  done  the  flow  of  current 
to  ground  or  between  the  wires  of  opposite  polarity  may  be- 
come quite  large.  Wires  lying  on  pipes  or  on  damp  wood- 
work, crossed  wires  or  live  parts  of  apparatus  mounted  on 
wooden  blocks,  all  tend  to  cut  down  the  insulation  resistance 
and  increase  the  leak.  The  effects  of  poor  insulation  are  :  First, 
it  represents  a  useless  loss  of  current,  and,  second,  and  more 
important,  it  means  a  possible  cause  of  fire. 

The  simplest  way  to  determine  the  insulation  resistance  of 
a  circuit  is  by  means  of  a  voltmeter.  In  Figure  29  if  a  volt- 
meter of  known  resistance  is  connected  between  one  side  of 
the  circuit  and  the  ground  and  there  is  a  ground  on  the  other 
side  of  the  circuit,  say  at  X,  current  will  flow  from  the  positive 
wire  through  the  voltmeter  then  through  the  ground  at  X  to 
the  negative  side  of  the  circuit.  The  voltmeter  needle  will 
indicate  a  certain  reading  which  we  will  call  V1.  If  the  volt- 
meter is  now  connected  directly  across  the  circuit  we  get  the 
circuit  voltage,  which  we  will  call  V.  The  two  readings,  V1 
and  V,  are  to  each  other  as  the  resistance  of  the  voltmeter 
is  to  the  combined  resistance  of  the  voltmeter  and  the  gnound 
at  X;  or,  calling  the  resistance  of  the  voltmeter  R  and  the  resist- 

yi          R  V  -  V1 

ance  of  the  ground  at  X  r,  we  get  —  = ,  or  r  —  R . 

V      R  +  r  V1 

As  an  example :  On  a  certain  system  the  voltage  across  the 
mains  is  110,  while  with  the  voltmeter  connected  as  shown  in 
Figure  29  we  obtain  a  reading  of  30.  The  resistance  of  the 
voltmeter  is  10,500  ohms.  Supplying  the  numbers  in  the  for- 


62 

mula 
groui 

MODERN   ELE< 
110-30 

r  —  10  500  """             ~~ 

:TRICAL  CONSTRUCTION. 

=  28,000  ohms  as  the  resistance  t 
of  the  system.    If  the  voltmeter 

30 
id  of  the  negative  side 

(J) 

HI" 

0       III* 

+ 

-^ 

+  _a    f 

«• 

r                                     -^            i                 - 

Figure  29  Figure  30 

connected  to  ground  from  the  other  side,  or  —  main,  the  resist- 
ance to  ground  of  the  +  side  can  be  obtained. 

If  both  sides  of  the  system  are  grounded  as  at  x  and  y, 
Figure  30  the  voltmeter  will  be  robbed  of  part  of  the  current 
which  would  pass  through  it  if  Y  were  not  in  parallel  with  it. 
It  will  therefore  not  indicate  correctly  under  such  circum- 
stances. 

If,  however,  tests  are  frequently  made  and  defects  cleared 
up   at   once   when   noticed,    it   will    seldom    happen   that   two 
grounds  occur  on  the  system  at  the 
same  time.    An  engineer  or  dynamo 
tender  will  soon  learn  what  the  in- 
sulation resistance  of  the  plant  in  his 
charge  should  be  and  be  governed  ac- 
cordingly. 

A  diagram  of  a  direct  current 
ground  detector  switch  is  shown  in 
Figure  31.  By  throwing  switch  A 
down  the  —  bus  bar  is  connected  to 
the  ground  through  the  voltmeter 
and  by  throwing  switch  B  the  +  bar 
is  connected  to  ground  through  the 
voltmeter.  The  ground  wire  should 
be  run  to  a  water  or  steam  pipe 


.p^rcu      LUC 

o 


i— Hffl 


MOTORS  63 

(never  to  a  gas  pipe)  or  to  some  grounded  part  of  the 
building.  If  no  good  ground  is  obtainable  one  may  be 
made  as  described  under  13  A. 

8.    Motors. 

a.  Must  be  thoroughly  insulated  from  the  ground  wherever 
feasible.  Wooden  base-frames  used  for  this  purpose,  and 
wooden  floors  which  are  depended  upon  for  insulation  where, 
for  any  reason,  it  is  necessary  to  omit  the  base-frames,  must 
be  kept  filled  to  prevent  absorption  of  moisture,  and  must  be 
kept  clean  and  dry. 

Where  frame  insulation  is  impracticable,  the  Inspection 
Department  having  jurisdiction  may,  in  writing,  permit  its 
omission,  in  which  case  the  frame  must  be  permanently  and 
effectively  grounded. 

A  high-potential  machine  which,  on  account  of  great  weight 
or  for  other  reasons,  cannot  have  its  frame  insulated,  should 
be  surrounded  with  an  insulated  platform.  This  may  be  made 
of  wood,  mounted  on  insulating  supports  and  so  arranged  that 
a  man  must  stand  upon  it  in  order  to  touch  any  part  of  the 
machine. 

In  case  of  a  machine  having  an  insulated  frame,  if  there  is 
trouble  from  static  electricity  due  to  belt  friction,  it  should  be 
overcome  by  placing  near  the  belt  a  metallic  comb  connected 
to  the  earth,  or  by  grounding  the  frame  through  a  very  high 
resistance  of  not  less  than  300,000  ohms. 

Where  motors  with  grounded  frames  are  operated  on  sys- 
tems where  one  side  is  either  purposely  or  accidentally 
grounded  there  exists  a  certain  difference  of  potential  be- 
tween the  windings  and  the  motor  frame ;  this  difference  of 
potential  depending  on  the  part  of  the  circuit  considered.  At 
some  places  in  the  winding  it  will  be  the  full  difference  of  po- 
tential at  which  the  motor  is  operating  and  at  other  points 
practically  nothing.  Should  the  conductors  accidentally  come 
in  contact  or  "ground"  on  the  motor  frame  a  short  circuit 
would  result,  as  the  circuit  would  then  be  completed  through 
the  motor  frame  and  ground.  To  obviate  this  the  motor  frame 
should  be  insulated  from  the  ground.  This  may  be  done  either 
by  setting  the  motor  on  a  wood  floor  or  by  the  use  of  a  base 


64  MODERN   ELECTRICAL  CONSTRUCTION. 

frame,  as  with  generators.  A  base  frame  should  always  be 
used  where  possible,  for  when  a  motor  is  set  directly  on  the 
floor  it  is  often  impossible  to  keep  the  space  under  it  clean,  and 
there  is  always  a  liability  of  the  floor  being  damp  or  of  nails 
in  the  floor  passing  through  the  woodwork  into  some  grounded 
part  of  the  building  or  metal  piping.  A  properly  constructed 
base  frame  will  allow  of  easy  cleaning  of  the  space  under  the 
motor. 

In  the  case  of  elevator  or  other  motors  where  the  shunt 
field  is  suddenly  broken,  a  momentarily  high  voltage  is  induced 
in  the  field  windings.  If  the  frame  of  the  motor  is  grounded 
this  high  voltage  has  a  strong  tendency  to  jump  through  the 
insulation  of  the  wires  to  the  metal  work  of  the  motor  thus 
grounding  the  circuit. 

b.  Must  be  wired  with  the  same  precautions  as  required 
by  rules  in  Class  "C"  for  wires  carrying  a  current  of  the  same 
volume  and  potential. 

Circuits  for  motors  may  be  -run  in  any  of  the  ways  described 
in  Class  "C" ;  either  open  on  knobs  or  cleats,  in  moulding, 
concealed  knob  and  tube  work  or  in  conduit ;  or  any  combina- 
tion of  these  may  be  used.  The  conditions  in  each  case  will  de- 
termine which  is  the  best  method  to  use.  Where  motors  are 
placed  some  little  distance  from  their  switches  and  starting 
boxes,  as  in  printing  press  work,  conduit  is  often  used  for 
the  wiring  between  the  switch  and  starting  box  and  the  motor. 
This  method  provides  very  good  mechanical  protection  for  the 
wires  and  affords  a  safe  way  of  running  them. 

The  motor  leads  or  branch  circuits  must  be  designed  to 
carry  a  current  at  least  twenty-five  per  cent,  greater  than  that 
for  which  the  motor  is  rated,  in  order  to  provide  for  the  in- 
evitable occasional  overloading  of  the  motor,  and  the  increased 
current  required  in  starting,  without  over-fusing  the  wires. 

The  use  of  voltages  above  550  is  rarely  advisable  or  neces- 
sary, and  will  only  be  approved  when  every  possible  safeguard 
has  been  provided.  Plans  for  such  installations  should  be  sub- 
mitted to  the  Inspection  Department  having  jurisdiction  before 
any  work  on  them  is  begun. 


MOTORS  65 

Good  values  to  use  for  calculating  the  size  of  wire  for 
branch  conductors  are  given  below.  The  question  of  loss  of 
voltage  is  not  taken  into  consideration  here. 

110  volts 9.3  amperes  per  horsepower 

220  volts 4.6  amperes  per  horsepower 

500  volts 2     amperes  per  horsepower 

For  mains  supplying  many  motors  it  is  not  necessary  to 
provide  the  twenty-five  per  cent,  overload  capacity,  because  it 
is  not  likely  that  all  motors  will  start  at  the  same  time.  If, 
however,  any  one  motor  has  more  than  half  the  capacity  of 
the  whole  installation,  it  is  advisable  to  provide  the  overload 
capacity.  For  instance,  if  two  motors,  each  of  50  amperes 
capacity,  are  fed  over  a  line  of  100  amperes  capacity  and 
one  is  started  while  the  other  is  working  at  full  load,  they  will 
overload  that  line  twelve  and  one-half  per  cent. 

For  mains  supplying  many  small  motors  the  size  should 
be  chosen  for  the  total  load  connected,  using  the  following 
values : 

110  volts 7.5    amperes  per  horsepower 

220  volts 3.75  amperes  per  horsepower 

500  volts 1.65  amperes  per  horsepower 

Where  there  are  a  number  of  110-volt  motors  installed  on 
the  Edison  3-wire  system,  providing  the  load  is  evenly  balanced 
between  the  two  sides,  the  mains  may  be  figured  as  though 
the  motors  were  operating  at  220  volts.  The  reason  for  this 
will  be  easily  seen  when  it  is  remembered  that  two  110-volt 
motors  operating  in  series  on  220  volts  (as  they  do  on  the 
Edison  3-wire  system)  take  only  one-half  the  current  they 
would  if  operated  on  a  straight  2- wire  110-volt  system. 

c.  Each  motor  and  resistance  box  must  be  protected  by  a 
cut-out  and  controlled  by  a  switch  (see  No.  17  a),  said  switch 
plainly  indicating  whether  "on"  or  "off."  With  motors  of  one- 
fourth  horsepower  or  less,  on  circuits  where  the  voltage  does 


MODERN   ELECTRICAL   CONSTRUCTION. 


not  exceed  300,  No.  21  d  must  be  complied  with,  and  single 
pole  switches  may  be  used  as  allowed  in  No.  22  c.  The  switch 
and  rheostat  must  be  located  within  sight  of  the  motor,  except 
in  cases  where  special  permission  to  locate  them  elsewhere  is 
given,  in  writing,  by  the  Inspection  Department  having  juris- 
diction. 

Where  the  crcuit-breaking  device  on  the  motor-starting 
rheostat  disconnects  all  wires  of  the  circuit,  the  switch  called 
for  in  this  section  may  be  omitted. 

Overload-release  devices  on  motor-starting  rheostats  will 
not  be  considered  to  take  the  place  of  the  cut-out  required  by 
this  section  if  they  are  inoperative  during  the  starting  of  the 
motor. 

The  switch  is  necessary  for  entirely  disconnecting  the  motor 
when  not  in  use,  and  the  cut-out  to  protect  the  motor  from 
excessive  currents  due  to  accidents  or  careless  handling  when 
starting.  An  automatic  circuit-breaker,  disconnecting  all  wires 
of  the  circuit  may,  however,  serve  as  both  switch  and  cut-out. 

For  the  larger  size  motors  a  cut-out  must  be  installed  for 
each  motor,  but  with  motors  of  J4  horsepower  or  less,  where 


Figure  32 

the  voltage  does  not  exceed  300,  a  cut-out  need  be  installed 
for  every  660  watts  only.  This  allows  about  5  1/8  horsepower 
motors,  31/6  horsepower  motors  or  2  %  horsepower  motors 


MOTORS  67 

on  one  cut-out.  .  Every  motor,  whether  large  or  small  must 
be  controlled  by  a  switch  which  will  indicate  whether  the  cur- 
rent is  on  or  off.  This  is  required  to  reduce  the  liability  of  a 
motor  being  accidentally  left  in  circuit,  which  might  result  in 
serious  trouble.  Figure  32  shows  a  complete  motor  installa- 
tion as  usually  arranged. 

As  a  general  rule  fused  knife  switches  are  used  for  the 
larger  motors,  while  with  the  smaller  motors  cut-out  blocks 
and  indicating  snap  switches  are  often  used.  If  the  motor  is 
J4  horsepower  or  less,  and  operated  on  a  circuit  where  the 
voltage  does  not  exceed  300,  a  single  pole  switch  may  be  used. 
For  all  motors  over  J4  horsepower,  and  for  all  motors  operated 
on  voltages  over  300,  double  pole  switches  must  be  used.  The 
object  of  locating  the  switch  and  starting  box  within  sight 
of  the  motor  is  that,  should  any  trouble  occur  when  the  motor 
is  being  started,  such  as  a  short  circuit  or  overload,  it  will 
be  immediately  noticed  and  the  current  shut  off.  If  the  con- 
ditions are  such  that  it  is  necessary  to  locate  the  motor  out 
of  sight  of  the  switch  and  starting  box  the  motor  should  be 
located  in  a  safe  place,  away  from  inflammable  material.  A 
special  permit  should  be  obtained  from  the  inspection  depart- 
ment having  jurisdiction  in  order  that  the  exact  conditions  may 
be  noted. 

d.  Must  have  their  rheostats  or  starting  boxes  located  so 
as  to  conform  to  the  requirements  of  No.  4. 

The  use  of  circuit  breakers  with  motors  is  recommended, 
and  may  be  required  by  the  Inspection  Department  having 
jurisdiction. 

To  be  safe  a  rheostat  should  have  as  great  a  carrying  ca- 
pacity as  the  motor  itself,  or  else  the  arm  should  have  a  strong 
spring-throw  attachment,  so  arranged  that  it  cannot  remain 
at  any  intermediate  position  unless  purposely  held  there. 
Specifications  governing  the  construction  of  rheostats  are  given 
in  No.  60. 

Starting  rheostats  and  auto-starters  should  be  treated  about 
the  same  as  knife-switches,  and  in  all  wet,  dusty  or  linty  places 
should  be  enclosed  in  dust-tight,  fireproof  cabinets.  If  a  special 
motor  room  is  provided,  the  starting  apparatus  and  safety  de- 
vices should  be  included  within  it.  Where  there  is  any  liability 


68  MODERN   ELECTRICAL  CONSTRUCTION. 

of  short  circuit  across  their  exposed  live  parts  being  caused  by 
accidental  contacts,  they  should  either  be  enclosed  in  cabinets, 
or  else  a  railing  should  be  erected  around  them  to  keep  un- 
authorized persons  away  from  their  immediate  vicinity. 

In  some  cities  the  local  rules  allow  the  starting  box  or 
rheostat  to  be  mounted  on  asbestos  board,  in  which  case  it 
must  be  mounted  out  from  the  wall  on  porcelain  knobs  so  that 
there  will  be  at  least  one  inch  air  space  between  the  wall 
and  the  current-carrying  parts.  If  the  starting  box  or  rheostat 
is  to  be  mounted  on  a  wall  or  other  support  where  the  frame 
would  be  grounded,  it  may  be  attached  to  a  wood  support  and 
the  wood  support  then  independently  attached  to  the  wall. 
The  best  construction  is  to  use  slate  or  marble.  If  slate  or 
marble  is  used  it  must  be  a  continuous  piece  which  will  entirely 
cover  the  space  back  of  the  rheostat  and  the  frame  of  the 
rheostat  should  be  screwed  to  the  slate  or  marble  and  the 
slate  or  marble  then  independently  screwed  to  the  wall,  never 
using  the  same  screw  for  attaching  both. 

A  starting  box  is  a  device  for  limiting  the  current  strength 
during  the  starting  of  the  motor  by  inserting  a  resistance  in 
series  with  the  armature.  The  ohmic  resistance  of  the  arma- 
ture of  a  shunt  or  compound  wound  motor  is  ordinarily  very 
small.  When  such  a  motor  is  at  rest  and  the  current  thrown 
directly  on,  the  full  voltage  is  thrown  across  the  small  resist- 
ance of  the  armature.  Consider  for  a  moment  the  case  of  a 
1  horespower  110  volt  motor  having  an  armature  resistance  of 
say  2  ohms,  and  taking,  when  running  normally,  8  amperes. 
Suppose  the  current  were  thrown  on  without  the  use  of  a 
starting  box.  According  to  Ohm's  law  the  current  through 
the  armature  would  be  110/2  —  55  amperes.  The  results,  were 
55  amperes  sent  through  the  armature,  can  easily  be  imagined. 
Now,  suppose  a  resistance  of  8  ohms  were  inserted  in  series 
with  the  armature  when  starting.  In  this  case  110/10=11 
amperes  only  would  have  to  pass  through  the  armature  and 
this  the  armature  can  easily  stand.  As  the  motor  begins  to 


revolve  a  counter  electro-motive  force  is  generated  which  op- 
poses the  inrush  of  current.  This  counter  electro-motive  force 
increases  until  the  motor  reaches  full  speed  and  takes  its  nor- 
mal current. 

In  the  example  given  above  at  the  first  step  of  the  starting 
box  there  will  be  a  current  of  11  amperes  flowing  through  a 
resistance  of  8  ohms  and  the  power  consumed  will  be  equal 
to  I2  R,  or  968  watts,  which  are  lost  in  heat  produced 
in  the  resistance  wire.  As  this  amounts  to  more  than  one 
horsepower  thrown  off  in  heat  the  advisability  of  mounting 
the  rheostat  away  from  inflammable  material  and  of  properly 
ventilating  it  can  readily  be  seen. 

Figure  33  shows  an  illustration  of  an  automatic  starting 
box,  and  a  diagram  of  the  connections  to  a  motor  circuit.  It 


Figure  33 

will  be  seen  that  the  resistance  coils  are  in  series  with  the 
armature  circuit.  As  the  arm  A  is  moved  to  the  right,  resist- 
ance is  gradually  cut  ont  of  the  armature  circuit  until  the 
arm  reaches  the  last  point,  where  it  is  automatically  held  in 


70 


MODERN   ELECTRICAL  CONSTRUCTION. 


position  by  means  of  the  small  magnet  M,  which  is  connected 
in  series  with  the  field  circuit.  By  tracing  out  the  circuits  it 
will  be  found  that  the  field  connection  is  made  on  the  first 
point  of  the  rheostat,  so  that  when  the  arm  A  is  in  the  "off" 
position  there  is  no  current  passing  through  the  field  coils. 


AAA/V 1 

— vwwws 


Figure  34 

It  will  also  be  noticed  that  the  last  contact  upon  which  the 
arm  rests  when  "off"  is  dead.  If  the  supply  current  for  any 
reason  fails,  current  will  cease  to  flow  around  the  coils  of  the 
magnet  M  and  it  will  become  demagnetized,  thus  allowing 
the  arm  A  to  fly  back  to  the  "off"  position.  This  overcomes 
the  possibility  of  the  main  current  being  momentarily  shut  off 
and  then  thrown  on  when  all  the  resistance  is  out  of  the  arma- 
ture circuit.  This  device  is  known  as  "no-voltage"  release. 

Another  device  known  as  the  "overload"  release  is  shown 
in  Figure  34,  with  a  diagram  of  the  connections.  The  wind- 
ing of  the  magnet  M1  carries  the  main  current.  When  the 
current  exceeds  a  certain  amount  (which  can  be  regulated 
by  a  small  nut)  the  armature  below  the  magnet  will 


MOTORS  71 

be  attracted,  thus  short  circuiting  the  coil  M  and  allowing 
the  arm  to  fly  back  and  shut  off  the  current  to  the  motor.  This 
device  cannot  be  considered  to  take  the  place  of  the  regular 
cut-outs,  as  it  is  not  operative  during  the  starting  of  the  motor. 
It  can  only  operate  after  the  arm  A  is  held  in  position  by  the 
magnet  M. 

Starting  boxes  are  made  in  different  designs  to  meet  the  re- 
quirements of  the  various  classes  of  work  on  which  they  are 
used.  Figure  35  shows  a  large  automatic  starting  box  where 
the  resistance  is  cut  out  by  the  action  of  the  solenoid  S,  which 


Figure  35 

draws  up  the  movable  arm.  When  solenoids  are  used  for  this 
purpose  it  is  often  advisable  to  arrange  the  connections  so  that 
when  the  movable  arm  has  been  raised  to  the  highest  and  last 
point  a  resistance  will  be  inserted  in  series  with  the  solenoid 
to  cut  down  the  current  and  reduce  the  heating  in  the  coil, 


72  MODERN   ELECTRICAL  CONSTRUCTION. 

as  less  current  is  required  to  hold  the  arm  in  place  than  to 
move  it  over  the  contacts.  Incandescent  lamps  are  often  used 
for  this  purpose  and  must  be  installed  as  in  4,  Class  A. 

A  speed  controller  differs  from  a  starting  box  mainly  in 
the  size  of  wire  used  as  resistance.    The  resistance  coils  of  a 


Figure  36 

starting  box  are  wound  with  comparatively  small  wire  con- 
nected in  circuit  for  a  short  time  only,  generally  from  ten  to 
twenty  seconds,  while  in  a  speed  controller  the  wire  must  be  of 
sufficient  size  to  carry  the  current  as  long  as  the  motor  is  run- 
ning. Another  difference  between  the  starting  box  and  speed 
controller  is  the  automatic,  coil,  (Fig.  33)  M,  which  in  the 
speed  controller  is  arranged  to  hold  the  arm  A  in  any  position 
in  which  it  may  be  placed.  This  is  accomplished  in  some  types 
of  speed  controllers  by  a  lever  attached  to  an  armature,  which. 


73 


is  attracted  by  the  magnet  M,  the  other  end  of  the  lever  fitting 
into  a  series  of  indentations  on  lower  part  of  movable  arm. 

While  the  underwriter's  rules  do  not  require  a  speed  con- 
troller to  be  automatic,  still  it  is  good  practice  to  make  them 
so,  as  the  same  principles  apply  to  the  starting  of  a  motor  with 
a  speed  controller  as  with  a  starting  box. 

Figure  36  shows  a  circuit  breaker  which  is  operative  during 
the  starting  of  the  motor,  and  can  be  used  to  take  the  place  of 
the  switch  required. 

As  the  arm  of  a  starting  box  or  speed  controller  is  moved 
from  one  contact  to  another,  more  or  less  sparking  results, 
and,  as  has  already  been  stated,  considerable  heat  is  developed 
in  the  coils.  A  rheostat  should  never  be  located  in  a  room 
where  either  inflammable  gases  or  dust  exist.  If  a  starting  box 
is  to  be  located  in  a  room  where  considerable  dirt  is  apt  to 
gather,  or  if  the  room  is  unusually  damp,  the  starting  box 
should  be  mounted  in  a  dust-tight  fire-proof  box,  which  should 


-en 

a— 


Figure  37 

be  kept  closed  at  all  times,  except  when  starting  the  motor.  If 
the  enclosing  box  is  rather  large,  sufficient  ventilation  of  the 
coils  will  be  obtained  while  the  motor  is  being  started  and  the 
door  open.  A  speed  controller  should  never  be  mounted  in  an 
enclosure  unless  the  same  is  arranged  to  give  a  thorough 
ventilation  to  the  outside  air,  as  heat  is  constantly  being  gen- 
erated in  the  coils  of  the  rheostat,  and  this  heat  must  be  dis- 


74  MODERN   ELECTRICAL  CONSTRUCTION. 

sipated.  A  speed  controller  should  never  be  located  where  dust 
or  lint  is  apt  to  gather  on  it.  If  it  is  necessary  to  use  one  on 
a  motor  located  in  such  a  place,  it  should  be  mounted  outside 
the  room. 

In  metal  working  establishments  or  in  any  place  where  there 
is  a  liability  of  the  contacts  on  the  switches  or  the  starting 
boxes  being  short-circuited,  they  should  be  enclosed  or  suitably 
protected. 

e.  Must  not  be  run  in  series-multiple  or  multiple-series, 
except  on  constant-potential  systems,  and  then  only  by  special 
permission  of  the  Inspection  Department  having  jurisdiction. 

Figure  37  shows  a  series-multiple,  and  Figure  38  a  multiple- 
series  system  of  wiring. 

/.     Must  be  covered  with  a  waterproof  cover  when  not  in 


Figure  38 

use,  and,  if  deemed  necessary  by  the  Inspection  Department 
having  jurisdiction,  must  be  enclosed  in  an  approved  case. 

From  the  nature  of  the  question  the  decision  as  to  what  is 
an  approved  case  must  be  left  to  the  Inspection  Department 
having  jurisdiction  to  determine  in  each  instance. 

When  it  is  necessary  to  locate  a  motor  in  the  vicinity  of 
combustibles  or  in  wet  or  very  dusty  or  dirty  places,  it  is  gen- 
erally advisable  to  surround  it  with  a  suitable  enclosure. 

The  sides  of  such  enclosure  should  preferably  be  made 
largely  of  glass,  so  that  the  motor  may  be  always  plainly 
visible.  This  lessens  the  chance  of  its  being  neglected,  and 
allows  any  derangement  to  be  at  once  noticed. 

Under  certain  conditions  it  is  found  necessary  to  enclose 
motors  in  dust-tight  enclosures.  The  practice  of  building  a 
small  box  which  fits  entirely  around  the  motor,  enclosing  the 


MOTORS  75 

pulley  and  provided  with  slots  through  which  the  belt  passes, 
is  very  unsatisfactory.  While  this  construction  prevents  con- 
siderable dust  from  settling  on  and  around  the  motor,  still  a 
great  deal  will  be  carried  in  by  the  belt.  If  the  box  is  so  made 
that  it  fits  tightly  around  the  shaft  between  the  pulley  and  the 
motor  frame  and  is  otherwise  well  constructed,  most  of  the  dust 
and  dirt  can  be  kept  out.  As  the  efficient  working  of  the  motor 
requires  that  it  be  kept  as  cool  as  possible,  the  box  should 
afford  sufficient  ventilation.  This  may  be  obtained  by  making 
the  box  somewhat  larger  than  the  motor,  thus  allowing  the  heat 
to  radiate  from  the  sides,  or  the  boxes  should  be  ventilated  to 
the  outside  air. 

A  number  of  motors  are  so  constructed  that,  by  means  of 
hand  plates,  they  can  be  entirely  enclosed.  When  they  are  so 
enclosed  their  efficiency  and  capacities  are  somewhat  reduced, 
but  cases  are  sometimes  found  where  the  conditions  require 
motors  of  this  kind  to  be  used. 

In  places  where  there  is  considerable  dust  flying  about  in 
the  air,  and  where  the  dust  is  not  readily  combustible,  a  fine 
gauze  can  be  used  to  close  the  hand  holes.  This  gauze  will 
allow  ventilation,  but  will  prevent  the  dirt  from  gathering 
inside  the  motor.  The  alternating  induction  motors,  which  are 
operated  without  brushes  or  collector  rings,  can  be  used  in 
almost  any  location,  as  there  is  no  sparking. 

g.  Must,  when  combined  with  ceiling  fans,  be  hung  from 
insulated  hooks,  or  else  there  must  be  an  insulator  interposed 
between  the  motor  and  its  support. 

Ceiling  fans  are  generally  provided  with  an  insulating  knob 
on  which  the  fan  hangs.  If  this  is  not  provided,  a  simple  knob 
break  can  be  used,  or  the  fan  can  be  suspended  from  a  hook 
screwed  into  a  hardwood  block,  provided  the  hook  does  not 
pass  through  the  block  into  the  plaster,  the  block  being  sep- 
arately supported  from  the  ceiling. 

h.     Must  each  be  provided  with  a  name-plate,  giving  the 


76  MODERN   ELECTRICAL  CONSTRUCTION. 

maker's  name,  the  capacity  in  volts  and  amperes,  and  the  nor- 
mal speed  in  revolutions  per  minute. 

9.  Railway  Power  Plants. 

a.  Each  feed  wire  before  it  leaves  the  station  must  be 
equipped  with  an  approved  automatic  circuit-breaker  (see  No. 
52)  or  other  device,  which  will  immediately  cut  off  the  current 
in  case  of  an  accidental  ground.  This  device  must  be  mounted 
on  a  fireproof  base,  and  in  full  view  and  reach  of  the  attendant. 

10.  Storage  or  Primary  Batteries. 

a.  When  current  for  light  and  power  is  taken  from  primary 
or  secondary  batteries,  the  same  general  regulations  must  be 
observed  as  apply  to  similar  apparatus  fed  from  dynamo  gen- 
erators developing  the  same  difference  of  potential. 

b.  Storage  battery  rooms  must  be  thoroughly  ventilated. 

c.  Special  attention  is  directed  to  the  rules  for  wiring  in 
rooms  where  acid  fumes  exist  (see  No.  24,  i  to  &). 

d.  All  secondary  batteries  must  be  mounted  on  non-absorp- 
tive, non-combustible  insulators,  such  as  glass  or  thoroughly 
vitrified  and  glazed  porcelain. 

e.  The  use  of  any  metal  liable  to  corrosion  must  be  avoided 
in  cell  connections  of  secondary  batteries. 

Rubber-covered  wire  run  on  glass  knobs  should  be  used  for 
wiring  storage  battery  rooms.  The  knobs  should  be  of  such 
size  as  to  keep  the  wire  at  least  one  inch  from  the  surface  wired 
over,  and  they  should  be  separated  2y2  inches  for  voltage  up 
to  300,  and  4  inches  for  voltages  over  300.  Waterproof  sockets 
hung  from  stranded  rubber  covered  wire  and  properly  sup- 
ported independently  of  the  joints  should  be  used ;  these  lights 
to  be  controlled  by  a  switch  placed  outside  of  battery  room. 
All  joints  after  being  properly  soldered  and  taped  with  both 
rubber  and  friction  tape  should  be  painted  with  some  good 
insulating  compound.  This  tends  to  keep  all  acid  fumes  away 
from  the  wire. 


TRANSFORMERS  77 

11.    Transformers. 

(For  construction  rules,  see  No.  62.) 
(See  also  Nos.  13,  130,  36.) 

a.  In  central  or  sub-stations  the  transformers  must  be  so 
placed  that  smoke  from  the  burning  out  of  the  coils  or  the 
boiling  over  of  the  oil  (where  oil  filled  cases  are  used)  could 
do  no  harm. 

If  the  insulation  in  a  transformer  breaks  down,  consider- 
ble  heat  is  likely  to  be  developed.  This  would  cause  a  dense 
smoke,  which  might  be  mistaken  for  a  fire  and  result  in 
water  being  thrown  into  the  building,  and  a  heavy  loss  there- 
by entailed.  Moreover,  with  oil  cooled  transformers,  espe- 
cially if  the  cases  are  filled  too  full,  the  oil  may  become 
ignited  and  boil  over,  producing  a  very  stubborn  fire. 


NOTICE-DO  NOT  FAIL  TO  SEE  WHETHER  ANY 
RULE  OR  ORDINANCE  OF  YOUR  CITY  CON- 
FLICTS WITH  THESE  RULES. 


CLASS  B. 
OUTSIDE  WORK. 

All  Systems  and  Voltages. 
12.     Wires. 

a.  Service  wires  must  have  an  approved  rubber  insulating 
covering  (see  No.  41).     Line  wires,  other  than  services,  must 
have  an  approved  weatherproof  or  rubber  insulating  covering 
(see  Nos.  41  and  44).     All  tie  wires  must  have  an  insulation 
equal  to  that  of  the  conductors  they  confine. 

In  risks  having  private  generating  plants,  the  yard  wires 
running  from  building  to  building  are  not  generally  consid- 
ered as  service  wires,  so  that  rubber  insulation  would  not  be 
required. 

By  service  wires  are  meant  those  wires  which  enter  the 
building.  It  is  customary  to  run  the  rubber-covered  wire  from 
the  service  switch  and  cutout  inside  of  building  through  the 
outer  walls,  and  to  leave  but  a  few  feet  of  wire  to  which  the 
line  wires  can  later  be  spliced.  This  is  illustrated  in  Figure  39, 
which  shows  how  wires  are  run  from  pole  to  building. 

b.  Must  be  so  placed  that  moisture  cannot  form  a  cross 
connection  between  them,  not  less  than  a  foot  apart,  and  not 
in  contact  with  any  substance  other  than  their  insulating  sup- 
ports.    Wooden  blocks  to  which  insulators  are  attached  must 
be  covered  over  their  entire  surface  with  at  least  two  coats  of 
waterproof  paint. 

c.  Must  be  at  least  7  feet  above  the  highest  point  of  flat 
roofs,  and  at  least  one  foot  above  the  ridge  of  pitched  roofs 
over  which  they  pass  or  to  which  they  are  attached. 

Roof  structures  are  frequently  found  which  are  too  low 
or  much  too  light  for  the  work,  or  which  have  been  carelessly 


OUTSIDE  WORK 


79 


put  up.  A  structure  which  is  to  hold  the  wires  a  proper 
distance  above  the  roof  in  all  kinds  of  weather  must  not  only 
be  of  sufficient,  height,  but  must  be  substantially  constructed 
of  strong  material 

It  is  well  to  avoid  fastening  wires  perpendicular  above  one 
another,  as  in  winter  icicles  may  form  which  extend  from  the 
top  to  the  lower  wire,  and  the  moisture  on  these  will  often 


Figure  39 

cause  much  trouble.  The  rule  requires  that  wires  be  7  feet 
above  flat  roofs,  and  roof  structures  must,  therefore,  be  made 
high  enough  to  allow  for  "sag."  In  moderately  long  runs 
2  or  3  feet  will  be  sufficient.  For  long  runs,  see  following  table, 
taken  from  construction  rules  of  Commonwealth  Electric  Com- 
pany of  Chicago : 

The  tension  on  wires  should  be  such  that  the  sag  of  a  span 
of  125  feet  will  not  exceed  the  amounts  shown. 

Temperature,  F...10    20    30    40    50    60    70    80    90 
Sag,  feet 6      8      8    10    10    12    12    14    14 

This  table  will  also  be  useful  to  consult  when  running  wires 
over  housetops  to  which  they  are  not  attached,  as  it  shows 
the  variation  in  "sag"  due  to  different  temperatures.  Wires 


MODERN   ELECTRICAL  CONSTRUCTION. 

should  be  so  run  that  even  at  the  highest  temperature  they  will 
still  clear  the  buildings.  Allowance  should  also  be  made  for 
the  gradual  elongation  of  the  wire  due  to  its  own  weight,  giving 
way  of  supports  or  sleet  that  may  at  times  weigh  it  down. 

d.  Must  be  protected  by  dead  insulated  guard  irons  or 
wires  from  possibility  of  contact  with  other  conducting  wires 
or  substances  to  which  current  may  leak.     Special  precautions 
of  this  kind  must  be  taken  where  sharp  angles  occur,  or  where 
any  wires  might  possibly  come  in  contact  with  electric  light 
or  power  wires. 

Crosses,  when  unavoidable,  should  be  made  as  nearly  at 
right  angles  as  possible. 

These  guard  wires  are  run  parallel  to  and  above  the  lower 
set  of  wires.  Their  object  is  to  prevent  the  upper  crossing 
wires,  should  they  break,  from  coming  in  contact  with  the 
lower.  A  separate  set  of  cross  arms  must  be  placed  on  the 
lower  poles  or  above  the  lower  wires  to  which  the  guard 
wires  must  be  fastened.  In  Figure  40  1  and  2  show  break  in- 
sulators that  may  be  used  to  electrically  disconnect  guard  wires. 

e.  Must  be  provided  with  petticoat  insulators  of  glass  or 
porcelain.     Porcelain  knobs  or  cleats  and  rubber  hooks  will 
not  be  approved. 

/.  Must  be  so  spliced  or  joined  as  to  be  both  mechanically 
and  electrically  secure  without  solder.  The  joints  must  then 
be  soldered,  to  insure  preservation,  and  covered  with  an 
insulation  equal  to  that  on  the  conductors. 

All  joints  must  be  soldered,  even  if  made  with  some  form 
of  patent  splicing  device.  This  ruling  applies  to  joints  and 
splices  in  all  classes  of  wiring  covered  by  these  rules. 

In  Figure  40  single  and  double  petticoat  insulators  are  shown. 
It  is  very  often  convenient  to  fasten  such  insulators  upside 
down  or  horizontally,  but  this  should  never  be  done,  as  they 
will  then  fill  with  water  or  dirt  and  their  insulating  qualities 
be  destroyed. 

g.  Must,  where  they  enter  buildings,  have  drip  loops 
outside,  and  the  holes  through  which  the  conductors  pass  must 


OUTSIDE   WORK 


81 


be    bushed    with    non-combustible,    non-absorptive    insuh  ting 
tubes  slanting  upward  toward  the  inside. 

7i.  Telegraph,  telephone  and  similar  wires  must  not  be 
placed  on  the  same  cross-arm  with  electric  light  or  power 
wires,  and  when  placed  on  the  same  pole  with  such  wires 
the  distance  between  the  two  inside  pins  of  each  cross-arm 
must  not  be  less  than  26  inches. 

i.  The  metallic  sheaths  to  cables  must  be  permanently 
and  effectively  connected  to  "earth." 

The  telephone  or  telegraph  wires  are  sometimes  placed 
above  the  power  wires,  and  it  very  often  becomes  necessary 


Figure  40 

for  a  lineman  to  pass  through  the  lower  wires  to  get  at  the 
tipper.  Great  care  is  necessary  to  avoid  coming  in  contact 
with  high  tension  power  wires  while  handling  the  telephone 
wires. 

Poles  should  not  be  set  more  than  125  feet  apart ;  100  or 
110  feet  is  good  practice.  For  small  wires  poles  with  6-inch 
tops  are  often  used,  but  for  heavier  wires  7-inch  tops  are 
advisable.  The  tops  of  pole  should  be  pointed,  so  as  to 
shed  water,  and  the  whole  pole  be  well  painted.  Steps  should 
be  placed  so  that  the  distance  between  any  two  steps  on  the 
same  side  is  not  over  36  inches ;  these  steps  should  all  be  the 
same  distance  apart,  and  should  not  extend  nearer  than  8  feet 
to  the  ground.  All  "gains"  cut  into  poles  should  be  painted 
before  cross-arms  are  placed  in  them.  Such  places  are  more 


82  MODERN   ELECTRICAL  CONSTRUCTION. 

likely  to  hold  moisture  and  rot  than  exposed  parts.  Wherever 
feed  wires  end  or  sharp  angles  occur,  double  cross-arms 
should  be  used,  fastened  on  opposite  sides  of  pole  and  bolted 
together. 

All  bolts,  lag  screws,  etc.,  should  be  galvanized.  Poles 
should  be  set  at  least  as  far  into  the  ground  as  shown  in  the 
following  table : 

Length  of  pole.     .  Depth  in  ground. 

35  feet  S1/,  feet 

40  "  6 

45  "  6 

50  "  6y2     " 

55  "  7 

60  "  8 

The  holes  should  be  large  enough  to  admit  of  thorough 
tamping  on  all  sides  of  bottom  of  hole.  If  the  tamping  at 
bottom  of  hole  is  not  well  done,  the  pole  will  always  be  shaky, 
no  matter  how  much  tamping  may  be  done  at  the  top.  If 
the  ground  is  soft,  the  pole  may  be  set  in  cement,  or  short 
pieces  of  planking  fastened  to  it  at  right  angles  underground. 
At  the  end  of  line  or  where  sharp  bends  occur,  strong  gal- 
vanized guy  cables  fastened  to  poles  six  or  eight  feet  long, 
buried  underground,  should  be  used. 

Trolley  Wires. 

/.  Must  not  be  smaller  than  No.  0  B.  &  S.  gage  copper 
or  No.  4  B.  &  S.  gauge  silicon  bronze,  and  must  readily  stand 
the  strain  put  upon  them  when  in  use. 

k.  Must  have  a  double  insulation  from  the  ground.  In 
wooden  pole  construction  the  pole  will  be  considered  as  one 
insulation. 

/.  Must  be  capable  of  being  disconnected  at  the  power 
plant,  or  of  being  divided  into  sections,  so  that,  in  case  of  fire 
on  the  railway  route,  the  current  may  be  shut  off  from  the 


OUTSIDE   WORK  83 

particular   section   and   not   interfere   with   the   work   of   the 
firemen.    This  rule  also  applies  to  feeders. 

m.  Must  be  safely  protected  against  accidental  contact 
where  crossed  by  other  conductors. 

Guard  wires  should  be  insulated  from  the  ground  and 
should  be  electrically  disconnected  in  sections  of  not  more 
than  300  feet  in  length. 

Ground  Return  Wires. 

«.  For  the  diminution  of  electrolytic  corrosion  of  under- 
ground metal  work,  ground  return  wires  must  be  so  arranged 
that  the  difference  of  potential  between  the  grounded  dynamo 
terminal  and  any  point  on  the  return  circuit  will  not  exceed 
twenty-five  volts. 

It  is  suggested  that  the  positive  pole  of  the  dynamo  be 
connected  to  the  trolley  line,  and  that  whenever  pipes  or  other 
underground  metal  work  are  found  to  be  electric-ally  positive 
to  the  rails  or  surrounding  earth,  that  they  be  connected  by 
conductors  arranged  so  as  to  prevent  as  far  as  possible  cur- 
rent flow  from  the  pipes  into  the  ground. 

12  A.     Constant-Potential  Pole  Lines,  Over  5,000  Volts. 

(Overhead  lines  of  this  class  unless  properly  arranged 
may  increase  the  fire  loss  from  the  following  causes : — 

Accidental  crosses  between  such  lines  and  low-potential 
lines  may  allow  the  high-voltage  current  to  enter  buildings 
over  a  large  section  of  adjoining  country.  Moreover,  such 
high  voltage  lines,  if  carried  close  to  buildings,  hamper  the 
work  of  firemen  in  case  of  fire  in  the  building.  The  object 
of  these  rules  is  so  to  direct  this  class  of  construction  that 
no  increase  in  fire  hazard  will  result,  while  at  the  same  time 
care  has  been  taken  to  avoid  restrictions  which  would  un- 
reasonably impede  progress  in  electrical  development. 

It  is  fully  understood  that  it  is  impossible  to  frame  rules 
which  will  cover  all  conceivable  cases  that  may  arise  in  con- 
struction work  of  such  an  extended  and  varied  nature,  and  it 
is  advised  that  the  Inspection  Department  having  jurisdiction 
be  freely  consulted  as  to  any  modification  of  the  rules  in  par- 
ticular cases.) 

a.    Every    reasonable    precaution    must    be    taken    in    ar- 


84  MODERN   ELECTRICAL   CONSTRUCTION. 

ranging  routes  so  as  to  avoid  exposure  to  contacts  with  other 
electric  circuits.  On  existing  lines,  where  there  is  a  liability 
to  contact,  the  route  should  be  changed  by  mutual  agreement 
between  the  parties  in  interest  wherever  possible. 

b.  Such  lines  should  not  approach  other  pole  lines  nearer 
than  a  distance  equal  to  the  height  of  the  taller  pole  line, 
and  such  lines  should  not  be  on  the  same  poles  with  other 
wires,    except    that    signalling    wires    used    by    the    Company 
operating  the  high-pressure  system,  and  which  do  not  enter 
property  other  than  that  owned   or  occupied  by  such   Com- 
pany, may  be  carried  over  the  same  poles. 

c.  Where  such  lines  must  necessarily  be  carried  nearer  to 
other  pole  lines  than  is  specified  in  Section  b  above,  or  where 
they   must   necessarily   be   carried   on   the    same   poles   with 
other   wires,   extra   precautions   to    reduce   the   liability   of   a 
breakdown  to  a  minimum  must  be  taken,  such  as  the  use  of 
wires  of  ample  mechanical  strength,  widely  spaced  cross-arms, 
short  spans,  double  or  extra  heavy  cross-arms,  extra  heavy 
pins,  insulators,  and  poles  thoroughly  supported.     If  carried 
on  the  same  poles  with  other  wires,  the  high-pressure  wires 
must  be  carried  at  least  three  feet  above  the  other  wires. 

d.  Where  such  lines  cross  other  lines,  the  poles  of  both 
lines  must  be  of  heavy  and  substantial  construction. 

Whenever  it  is  feasible,  end-insulator  guards  should  be 
placed  on  the  cross-arms  of  the  upper  line.  If  the  high- 
pressure  wires  cross  below  the  other  lines,  the  wires  of  the 
upper  line  should  be  dead-ended  at  each  end  of  the  span  to 
double-grooved,  or  to  standard  transposition  insulators,  and 
the  line  completed  by  loops. 

One  of  the  following  forms  of  construction  must  then  be 
adopted : 

1.  The  height  and  length  of  the  cross-over  span  may 
be  made  such  that  the  shortest  distance  between  the 
lower  cross-arms  of  the  upper  line  and  any  wire 
of  the  lower  line  will  be  greater  than  the  length 
of  the  cross-over  span,  so  that  a  wire  breaking 
near  one  of  the  upper  pins  would  not  be  long 
enough  to  reach  any  wire  of  the  lower  line.  The 
high-pressure  wires  should  preferably  be  above  the 
other  wires. 


OUTSIDE  WORK  85 

2.  A  joint  pole  may  be  erected  at  the  crossing  point, 

high-pressure  wires  being  supported  on  this  pole 
at  least  three  feet  above  the  other  wires.  Mechan- 
ical guards  or  supports  must  then  be  provided,  so 
that  in  case  of  the  breaking  of  any  upper  wire,  it 
will  be  impossible  for  it  to  come  into  contact  with 
any  of  the  lower  wires. 

Such  liability  of  contact  may  be  prevented  by 
the  use  of  suspension  wires,  similar  to  those  em- 
ployed for  suspending  aerial  telephone  cables, 
which  will  prevent  the  high-pressure  wires  from 
falling  in  case  they  break.  The  suspension  wires 
should  be  supported  on  high-potential  insulators, 
should  have  ample  mechanical  strength,  and  should 
be  carried  over  the  high-pressure  wires  for  one  span 
on  each  side  of  the  joint  pole,  or  where  suspension 
wires  are  not  desired  guard  wires  may  be  carried 
above  and  below  the  lower  wires  for  one  span  on 
each  side  of  the  joint  pole,  and  so  spread  that  a 
falling  high-pressure  wire  would  be  held  out  of 
contact  with  the  lower  wires 

Such  guard  wires  should  be  supported  on  high- 
potential  insulators  or  should  be  grounded.  When 
grounded,  they  must  be  of  such  size,  and  so  con- 
nected and  earthed,  that  they  can  surely  carry  to 
ground  any  current  which  may  be  delivered  by  any 
of  the  high-pressure  wires.  Further,  the  construc- 
tion must  be  such  that  the  guard  wires  will  not 
be  destroyed  by  any  arcing  at  the  point  of  contact 
likely  to  occur  under  the  conditions  existing. 

3.  Whenever  neither  of  the  above  methods  is  feasible, 

a  screen  of  wires  should  be  interposed  between 
the  lines  at  the  cross-over.  This  screen  should  be 
supported  on  high  tension  insulators  or  grounded 
and  should  be  of  such  construction  and  strength 
as  to  prevent  the  upper  wires  from  coming  into 
contact  with  the  lower  ones. 

If  the  screen  is  grounded  each  wire  of  the  screen 
must  be  of  such  size  and  so  connected  and  earthed 
that  it  can  surely  carry  to  ground  any  current 
which  may  be  delivered  by  any  of  the  high  pressure 
wires.  Further,  the  construction  must  be  such  that 
the  wires  of  screen  will  not  be  destroyed  by  any 
arcing  at  the  point  of  contact  likely  to  occur  under 
the  conditions  existing. 

e.  When  it  is  necessary  to  carry  such  lines  near  buildings, 
they  must  be  at  such  height  and  distance  from  the  building 
as  not  to  interfere  with  firemen  in  event  of  fire;  therefore,  if 


86  •       MCDEIIN   ELZCTr.ICAL   CONSTRUCTION. 

wi'.hin  25  feet  of  a  building,  they  irvst  be  carried  at  a  height 
ret  less  lhan  that  of  the  front  cornice,  a::d  the  height  must  be 
greater  than  that  of  the  cornice,  as  the  wires  come  nearer  to 
the  building,  in  accordance  with  the  following  table : — 

Distance  of  wire  Elevation  of  wire 
from  building.                                 above  cornice  of  building. 

Feet.  Feet. 

25  0 

20  2 

15  4 

10  6 

5  8 

2%  9 

Tt  Is  evident  that  where  the  roof  of  the  building  continues 
nearly  in  line  with  the  walls,  as  in  Mansard  roofs,  the  height 
and  distance  of  the  line  must  be  reckoned  from  some  part  of 
the  roof  instead  of  from  the  cornice. 

13.    Transformers. 

(For  construction  rules,  see  No.  62.) 
(See  also  Nos.  n,  13  A  and  36.) 

Where  transformers  are  to  be  connected  to  high-voltage 
circuits,  it  is  necessary  in  many  cases,  for  best  protection  to 
life  and  property,  that  the  secondary  system  be  permanently 

f rounded,  and  provision  should  be  made  for  it  when  the  trans- 
ormers   are    built. 

a.  Must  not  be  placed  inside  of  any  building  excepting 
central  stations,  unless  by  special  permission  of  the  Inspection 
Department  having  jurisdiction. 

An  outside  location  is  always  preferable;  first,  because  It 
keeps  the  high-voltage  primary  wires  entirely  out  of  the 
building,  and  second,  for  the  reasons  given  in  the  note  to 
No.  11  a. 

b.  Must  not  be  attached  to  the  outside  walls  of  buildings, 
unless  separated  therefrom  by  substantial  supports. 

The  alternating  current  transformer  consists  of  an  iron 
core  upon  which  wires  of  two  distinct  electrical  circuits  are 
wound.  One  of  these  is  known  as  the  primary  circuit,  and  in 
it  the  high  pressure  currents  coming  direct  from  the  dynamo 
circulate.  The  other  is  known  as  the  secondary  circuit,  and 
in  it  the  low  pressure  currents  used  inside  of  buildings  circu- 


GROUNDING 


87 


late.  These  two  circuits  are  wound  generally  one  over  the 
other,  and  are  very  close  together.  The  pressure  used  in  the 
primary  coil  is  from  1,000  to  5,000  volts,  while  in  the  secondary 
it  is  reduced  usually  to  110  or  220. 

It  quite  frequently  happens  that  the  insulation  between  the 
two  windings  breaks  down  and  thus  the  high  pressure  is  acci- 
dentally brought  into  buildings.  Under  such  circumstances 
should  any  one  touch  any  live  part  of  the  installation  while 
touching  also  grounded  parts  of  the  building  death  would  very 
likely  result.  Also,  should  there  be  a  weak  spot  in  the  insula- 
tion, it  is  quite  likely  the  high  pressure  would  pierce  it  at  that 
point  with  a  possible  result  of  a  fire.  Many  deaths  and  fires 


Figure  41 

have  been  caused  in  this  way.  If  such  lines  are  connected  to 
ground  the  chances  for  harm  are  very  much  lessened,  for  the 
current  will  never  take  the  path  of  high  resistance  through 
a  man's  body,  while  a  direct  path  through  a  low  resistance  wire 
is  open  to  it. 

It  must  not  be  supposed  that  "grounding"  one  side  of  an 
electric  light  system  is  not  often  followed  by  serious  conse- 


88  MODERN   ELECTRICAL   CONSTRUCTION. 

quences,  for  under  such  circumstances  a  ground  coming  on  any 
other  part  of  the  system  will  cause  a  short  circuit  at  once. 
The  grounding  in  these  cases  is  to  be  looked  upon  as  the  lesser 
of  two  evils  rather  than  as  an  advantage.  With  alternating 
currents,  the  chances  of  possible  damage  from  grounding 
are  much  less  than  with  direct  currents,  because  each  trans- 
former with  its  small  group  of  lamps  is  a  system  by  itself  and 
not  affected  by  grounds  on  other  transformers.  Thus  a  5,000 
light  alternating  current  installation  would  consist  of  from 
25  to  50  separate  systems,  each  independent  of  defects  on  the 
rest,  while  in  a  continuous  current  installation,  a  ground  on  the 
most  remote  branch  circuit  would  in  conjunction  with  a 
ground  on  the  opposite  pole  of  any  other  part  of  the  system 
form  a  short  circuit. 

Methods  of  grounding  secondary  wires  of  alternating  cur- 
rent transformers  are  shown  in  Figure  41,  taken  from  an 
instruction  book  issued  by  the  Commonwealth  Electric  Com- 
pany of  Chicago. 

In  connection  with  3-wire  systems,  grounding  of  the  neutral 
wire  can  do  little  harm,  because  ordinarily  the  neutral  wire 
seldom  carries  much  current,  and  that  current  is  apt  to  vary 
in  direction  so  that  the  electrolytic  effect  will  be  on  the  whole 
quite  negligible. 

There  is,  of  course,  the  hazard  brought  about  by  the  fact 
that  a  ground  coming  on  one  of  the  outside  wires  will  imme- 
diately form  a  short-circuit  in  connection  with  the  ground  on 
the  neutral. 

In  connection  with  3-wire  systems,  however,  it  is  of  the 
greatest  importance  (as  more  fully  explained  further  on)  that 
the  neutral  wire  remain  intact,  and  it  being  thoroughly 
grounded  at  all  available  outside  places  will  help  to  keep  it  so. 

13  A.     Grounding  Low-Potential  Circuits. 

The  grounding  of  low-potential  circuits  under  the  follow- 


GROUNDING.  89 

Ing  regulations  Is  only  allowed  when  such  circuits  are  so  ar- 
ranged that  under  normal  conditons  of  service  there  will  be 
no  passage  of  current  over  the  ground  wire. 

Direct-Current  3-Wire  System. 

a.  Neutral  wire  may  be  grounded,   and   when  grounded 
the  following  rules  must  be  complied  with : — 

1.  Must  be  grounded  at  the  Central  Station  on  a  metal 

plate  buried  in  coke  beneath  permanent  moisture 
level,  and  also  through  all  available  underground 
water  and  gas-pipe  systems. 

2.  In  underground  systems  the  neutral  wire  must  also  be 

grounded  at  each  distributing  box  through  the  box. 

3.  In    overhead    systems    the     neutral     wire     must     be 

grounded  every  500  feet,  as  provided  in  Sections 
c,  c,  f  and  g. 

Inspection  Department  having  jurisdiction  may  require 
grounding  if  they  deem  It  necessary. 

Two-wire  direct-current  systems  having  no  accessible  neu- 
tral point  are  not  to  be  grCunded. 

Alternating-Current  Secondary  Systems. 

b.  Transformer      secondaries      of      distributing      systems 
should  preferably  be  grounded,  and  when  grounded,  the  follow- 
ing rules  must  be  complied  with : — 

1.  The  grounding  must  be  made  at  the  neutral  point  or 

wire,  whenever  a  neutral  point  or  wire  is  accessible. 

2.  When  no  neutral  point  or  wire  is  accessible,  one  side 

of  the  secondary  circuit  may  be  grounded,  pro- 
vided the  maximum  difference  of  potential  between 
the  grounded  point  and  any  other  point  in  the  circuit 
does  not  exceed  250  volts. 

3.  The  ground  connection  must  be  at  the  transformer 

as  provided  in  sections  d,  c,  f,  g,  and  when  trans- 
formers feed  systems  with  a  neutral  wire,  the  neu- 
tral wire  must  also  be  grounded  at  least  every  250 
feet  for  overhead  systems,  and  every  500  feet  for 
underground  systems. 

Inspection  Departments  having  jurisdiction  may  require 
grounding  if  they  deem  it  necessary. 


90  MODERN   ELECTRICAL   CONSTRUCTION. 

Ground  Connection. 

c.  The  ground  wire  in  direct-current  3-wire  systems  must 
not  at  Central  Stations  be  smaller  than  the  neutral  wire  and 
not  smaller  than  No.  6  B.  &  S.  gage  elsewhere. 

d.  The  ground  wire  in  alternating-current  systems  must 
never  be  less  than  No.  6  B.  &  S.  gage,  and  must  always  have 
equal  carrying  capacity  to  the  secondary  lead  of  the  trans- 
former, or  the  combined  leads  where  transformers  are  con- 
nected in  parallel. 

On  three  phase  systems,  the  ground  wire  must  have  a 
carrying  capacity  equal  to  that  of  any  one  of  the  three  mains. 

c.  The  ground  wire  must  be  kept  outside  of  buildings,  but 
may  be  directly  attached  to  the  building  or  pole.  The  wire 
must  be  carried  in  as  nearly  a  straight  line  as  possible,  and 
kinks,  coils  and  sharp  bends  must  be  avoided. 

/.  The  ground  connection  for  Central  Stations,  trans- 
former substations,  and  banks  of  transformers  must  be  made 
through  metal  plates  buried  in  coke  below  permanent  mois- 
ture level,  and  connection  should  also  be  made  to  all  available 
underground  piping  systems  including  the  lead  sheath  of  under- 
ground cables. 

g.  For  individual  transformers  and  building  services  the 
ground  connection  may  be  made  as  in  Section  f,  or  may  be 
made  to  water  or  other  piping  systems  running  into  the  build- 
ings. This  connection  may  be  made  by  carrying  the  ground 
wire  into  the  cellar  and  connecting  on  the  street  side  of  meters, 
main  cocks,  etc.,  but  connection  must  never  be  made  to  any 
lead  pipes  which  form  part  of  gas  services. 

In  connecting  a  ground  wire  to  a  piping  system,  the  wire 
should,  if  possible,  be  soldered  into  a  brass  plug  and  the  plug 
forcibly  screwed  into  a  pipe-fitting,  or,  where  the  pipes  are 
cast  iron,  into  a  hole  tapped  into  the  pipe  itself.  For  large 
stations,  where  connecting  to  underground  pipes  with  bell 
and  spigot  joints,  it  is  well  to  connect  to  several  lengths,  as 
the  pipe  joints  may  be  of  rather  high  resistance.  Where  plugs 
cannot  be  used,  the  surface  of  the  pipe  may  be  filed  or  scraped 
bright,  the  wire  wound  around  it,  and  a  strong  clamp  put 
over  the  wire  and  firmly  bolted  together. 

Where  ground  plates  are  used,  a  No.  16  Stubbs'  gage 
copper  plate,  about  three  by  six  feet  in  size,  with  about  two 
feet  of  crushed  coke  or  charcoal,  about  pea  size,  both  under 
ana  over  it,  would  make  a  ground  of  sufficient  capacity  for  a 


GROUND   PLATES.  91 

moderate-sized  station,  and  would  probably  answer  for  the 
ordinary  substation  or  bank  of  transformers.  For  a  large 
central  station,  a  plate  with  considerably  more  area  might 
be  necessary,  depending  upon  the  other  underground  con- 
nections available.  The  ground  wire  should  be  riveted  to 
the  plate  in  a  number  of  places,  and  soldered  for  its  whole 
length.  Perhaps  even  better  than  a  copper  plate  is  a  cast- 
iron  plate  with  projecting  forks,  the  idea  of  the  fork  being 
to  distribute  the  connection  to  the  ground  over  a  fairly  broad 
area,  and  to  give  a  large  surface  contact.  The  ground  wire 
can  probably  best  be  connected  to  such  a  cast-iron  plate  by 
soldering  it  into  brass  plugs  screwed  into  holes  tapped  in  the 
plate.  In  all  cases,  the  joint  between  the  plate  and  the  ground 
wire  should  be  thoroughly  protected  against  corrosion  by 
painting  it  with  waterproof  paint  or  some  equivalent. 


NOTE.-DO  NOT  FAIL  TO  SEE  WHETHER  ANY 
RULE  OR  ORDINANCE  OF  YOUR  CITY  CONFLICTS 
WITH  THESE  RULES. 

CLASS  C. 

INSIDE  WORK. 
All  Systems  and  Voltages. 

GENERAL   RULES. 

14.    Wires. 

(For  special  rules,  see  Nos.  18,  24,  35,  38  and  39.) 

a.  Must  not  be  of  smaller  size  than  No.  14  B.  &  S.  gage, 
except  as  allowed  under  Nos.  24  v  and  45b. 

The  exceptions  being  wires  used  inside  of  fixtures  and 
flexible  cord  used  to  suspend  individual  electric  lights.  For 
general  purposes  a  wire  smaller  than  No.  14  is  too  easily 
broken,  either  through  a  sharp  kink,  or  by  drawing  too  tight 
with  tie  wires.  To  avoid  trouble  from  kinks  or  sharp  bends, 
wires  smaller  than  14  should  preferably  be  stranded. 

b.  Tie  wires  must  have  an  insulation  equal  to  that  of  the 
conductors  they  confine. 

This  is  considered  necessary,  because  very  often  the  tie 
wire  cuts  through  the  insulation  of  the  wire  it  confines,  and  if 
the  tie  wire  should  come  in  contact  with  other  than  its  insu- 
lating support,  there  would  still  be  good  insulation.  In  Figure 
42,  (1)  and  (2)  illustrate  the  method  of  tieing  usually  employed 
with  small  wires  on  insulators ;  (4)  shows  a  method  employed 
with  larger  wires.  This  is  also  especially  useful,  because  slack 
can  be  taken  up  if  the  tie  wire  is  arranged  to  draw  the  main 
wire  about  half  way  around  the  insulator;  (6)  shows  a  knot 
tied  into  the  wire,  as  is  usual  where  the  end  of  the  wire 


INSIDE  WORK. 


93 


connects  into  cut-outs  or  switches.  At  (5)  insulators  are 
arranged  to  hold  large  wires.  It  is  not  advisable  to  tie  large 
wires  to  insulators,  as  the  weight  of  the  wire  will  soon  cause 


Figure  42 


Cleats,  such  as  shown  at  (8) 


it  to  cut  through  the  insulation, 
and  (9),  are  preferable. 

c.     Must  be  so  spliced  or  joined  as  to  be  both  mechanically 
and  electrically  secure  without  solder.    The  joints  must  then 


94 


MODERN   ELECTRICAL  CONSTRUCTION. 
C 


Figure  43 


INSIDE  WORK.  95 

be  soldered  to  insure  preservation,  and  covered  with  an  insu- 
lation equal  to  that  on  the  conductors. 

Stranded  wires  must  be  soldered  before  being  fastened 
under  clamps  or  binding  screws,  and  whether  stranded  or 
solid,  when  they  have  a  conductivity  greater  than  that  of  No. 
8  B.  &  S.  gage  they  must  be  soldered  into  lugs  for  all  terminal 
connections. 


All  joints  must  be  soldered,  even  if  made  with  some  form 
of  patent  splicing  device.  This  ruling  applies  to  joints  and 
splices  in  all  classes  of  wiring  covered  by  these  rules. 

At  the  left  on  top  of  Fig.  43  is  shown  the  well-known 
Western  Union  joint.  Before  joining  wires  they  should  be 
thoroughly  cleaned  by  scraping  with  the  back  of  a  knife  or 
sand  or  emery  paper.  The  insulation  should  be  removed,  as 
indicated  at  b;  if  it  is  cut  into  as  at  a,  it  is  very  likely  that 
the  wire  will  be  "nicked"  and  will  be  likely  to  break  at  that 
point.  It  is  also  more  difficult  to  tape  a  joint  properly  if  the 
rubber  has  been  cut  in  this  way  than  it  is  with  the  rubber  cut 
as  at  b.  After  the  joint  has  been  made  it  is  covered  with 
soldering  fluid,  a  formula  for  which  is  given  below.  In  lieu 
of  this  there  are  soldering  sticks  and  salts,  already  prepared, 
on  the  market. 

The    following    formula    for    soldering    fluid    is    sug- 
gested : — 

Saturated    solution   of   zinc    chloride 5  parts 

Alcohol     4   parts 

Glycerine     1   part 

The  joint  having  been  thoroughly  covered  with  one  of 
these  preparations  is  next  heated  with  a  gasoline  or  alcohol 
torch  and  a  small  piece  of  solder  allowed  to  melt  on  it  near 
the  center.  It  is  well  to  avoid  heating  too  much  at  the  ends 
of  the  joint,  as  it  weakens  the  wire.  After  the  joint  is  cool, 
wipe  off  all  moisture  and  cover  with  layers  of  rubber  tape, 
enough,  at  least,  so  that  it  is  equal  in  thickness  to  the  rubber 
insulation  on  the  wire  used,  as  shown  at  a  and  b.  This  rubber 


96  MODERN   ELECTRICAL   CONSTRUCTION. 

tape  is  then  covered  with  friction  tape  to  keep  it  in  place. 
Before  taping  joints  the  outer  braid  of  the  wire  should  be 
carefully  skinned  back.  If  any  of  the  cotton  threads  of  which 
it  consists  were  to  be  left  in  contact  with  the  bare  wire,  they 
would,  when  moist,  form  a  leak,  which  might  prove  trouble- 
some. If  joints  are  exposed  to  the  weather  it  will  be  well  to 
paint  them  over  with  some  insulating  paint  to  keep  the  friction 
tape  in  place,  as  it  will  otherwise  soon  work  loose  when  it 
becomes  dry. 

At  c  and  d  "tap"  joints  are  shown.  The  method  shown 
at  d  is  preferable,  because  the  wire  cannot  easily  work  loose. 
The  method  of  joining  shown  at  c  is  useful  when,  for  instance, 
two  wires,  each  of  which  is  fastened  to  an  insulator,  are  to  be 
joined.  The  wires  c?n  be  drawn  very  tight  in  this  way. 
This  sort  of  joint  is  very  common  in  fixture  work,  and  should 
be  finished  off  as  at  f. 

Twin  wires  other  than  flexible  cord  are  allowed  only  in 
metal  conduits,  and  joints  in  them  should  be  made  only  within 
the  junction  boxes.  When  joints  in  conduit  are  unavoidable, 
twin  wires  should  be  joined  as  at  g,  so  that  the  joints  are  not 
opposite  each  other.  Joints  in  flexible  cord  should  be  avoided 
as  much  as  possible. 

In  splicing  stranded  wires  it  is  customary  to  remove  some 
of  the  center  strands  to  avoid  making  a  very  bulky  splice.  All 
stranded  wires  must  be  soldered  where  fastened  under  binding 
screws;  this  refers  also  to  flexible  cord  used  in  sockets.  The 
best  way  to  solder  the  ends  of  cords  is  to  dip  them  in  melted 
solder;  a  blow  torch  will  easily  overheat  small  wires  and 
leave  them  brittle. 

Figure  44  shows  lead  covered  wire  spliced  and  taped.  In 
handling  lead  covered  wire  great  care  must  be  exercised 
(especially  with  paper  insulated)  that  it  be  not  bruised  and  the 
lead  not  punctured.  The  lead  covering  is  of  use  only  as  a 
protection  against  water;  if  it  admits  the  least  bit  of  moisture 


INSIDE   WORK.  97 

it  is  worse  than  useless.  The  ends  of  lead  covered  wires 
should  always  be  kept  sealed  until  ready  for  use;  in  damp 
places  the  paper  insulation  may  absorb  moisture,  which  will 
ground  the  wire  on  the  lead.  When  installed  the  ends  should 
always  be  sealed  against  moisture.  Lead  covered  wires 
should  never  be  used  where  there  is  a  liability  of  nails  being 
driven  into  them. 

Joints  in  lead  covered  wires  are  made  just  as  in  ordinary 
wires.     Extreme  care  is  necessary  that  no  moisture  be  left  on 


Figure  44 

the  wire  when  it  is  taped  or  covered  up.  Before  the  wire  is 
joined  a  sleeve  (Figure  44)  is  slipped  over  one  of  the  wires. 
After  the  joint  has  been  made  and  taped,  this  sleeve  is  placed 
so  as  to  cover  it,  and  the  ends  split  and  arranged  to  fit  close 
against  the  lead  on  the  wires.  That  part  of  the  lead  which 
must  be  soldered  to  make  the  joint  watertight  is  scraped  until 
it  is  perfectly  bright  and  then  coated  with  tallow  candle  grease. 
It  can  then  be  soldered  with  an  iron,  or  melted  solder  can  be 
poured  on  it  and  wiped  around  it,  as  plumbers  do.  If  a 
soldering  iron  is  used  it  must  not  be  too  hot,  and  not  allowed 
to  remain  in  one  place  too  long,  as  the  lead  itself  melts  at 
nearly  the  same  temperature  as  the  solder.  An  inexperienced 
workman  may  burn  more  holes  into  the  lead  than  he  closes. 
If  a  neat  job  is  desired,  that  part  of  the  lead  which  is  to  be  kept 
free  of  solder  is  covered  with  lampblack  and  glue,  or  ordinary 
paper  hanger's  paste,  or  a  mixture  of  flour  and  water  boiled, 
so  as  to  prevent  the  solder  from  taking  on  it. 

d.     Must   be    separated    from    contact    with    walls,    floors, 
timbers  or  partitions  through  which  they  may  pass  by  non- 


98 


MODERN    ELECTRICAL   CONSTRUCTION. 


combustible,  non-absorptive  insulating  tubes,  such  as  glass  or 
porcelain,  except  as  provided  in  No.  24  «. 

Bushings  must  be  long  enough  to  bush  the  entire  length 
of  the  hole  in  one  continuous  piece  or  else  the  hole  must 
first  be  bushed  by  a  continuous  waterproof  tube.  This  tube 
may  be  a  conductor,  such  as  iron  pipe,  but  in  that  case  an 
insulating  bushing  must  be  pushed  into  each  end  of  It,  ex- 
tending far  enough  to  keep  the  wire  absolutely  out  of  contact 
with  the  pipe. 

The  exception  mentioned  is  in  regard  to  wires  at  outlets 
where  they  are  required  to  be  in  approved  flexible  tubing  from 
the  last  insulator  to  at  least  one  inch  beyond  plaster,  or  end 
of  the  cap  on  gas  piping.  This  is  shown  in  Figure  45.  The 
reason  for  the  separation  of  wires  from  everything  but  their 
insulating  supports  are  many.  Should  a  bare  live  wire  come 
in  contact  with  damp  woodwork  or  masonry,  there  would 


Figure  45 

very  likely  be  some  flow  of  current  to  ground  and  through  the 
ground  to  the  other  pole  of  the  dynamo  or  other  wire.  This 
flow  of  current  may  gradually  char  the  woodwork,  and  in 
time  start  a  fire ;  or  it  may  gradually  eat  away  the  wire,  finally 
causing  it  to  break.  When  a  wire  is  eaten  away,  as  shown 


INSIDE   WORK. 


99 


at  c  and  e,  Figure  46,  if  it  is  carrying  much  current,  the  thin 
part  will  become  very  hot  and  will  set  fire  to  whatever  inflam- 
mable material  may  be  near  it.  If  the  current  flow  to  the 
ground  continues,  the  positive  wire  will  finally  be  entirely 
severed,  and  an  arc,  similar  to  that  noticed  in  an  ordinary  arc 
lamp,  will  be  established,  and  will  continue  until  the  wire  has 


Figure 


been  burned  away  and  the  space  between  the  two  ends  becomes 
too  great  for  the  arc  to  maintain  itself.  The  negative  wire, 
to  which  the  current  flows,  is  not  eaten  away  in  this  manner, 
and  such  current  flow  is  only  possible  when  two  wires  of  a 
system  are  in  electrical  connection  with  the  ground.  This 
action  may,  however,  occur,  even  if  the  two  grounded  wires 
are  miles  apart.  Wires  and  gas  pipes  are  often  destroyed 
through  intermittent  contact;  for  instance,  if  a  wire  makes  a 
good  contact  to  a  gas  pipe  and  there  is  a  small  leak  to  the  pipe 
no  particular  harm  will  be  done  as  long  as  the  contact  remains 
good.  Should,  however,  the  contact  be  intermittent,  there  will 
be  a  small  arc  at  each  break,  and  this  will,  little  by  little,  burn 
holes  into  the  gas  pipe  and  into  the  wire.  This  action  will 
take  place  on  either  a  positive  or  negative  wire.  Non-com- 


100  MODERN   ELECTRICAL  CONSTRUCTION. 

bttstible  supports  for  wires  are  farther  useful  in  that  they 
tend  to  prevent  flames  from  the  rubber  insulation  (which  is 
very  easily  ignited  from  any  of  the  above  causes)  from  spread- 
ing to  surrounding  material. 

Figure  46  consists  of  copies  of  specimens  showing  effects 
of  electrolysis,  short  circuits,  and  heating  of  lamp.  These 
illustrations  are  copied  from  fire  reports  of  the  National  Board 
of  Underwriters. 

At  a  is  shown  a  piece  of  gas  pipe,  which  had  been  subject 
to  electrolytic  action  until  finally  a  hole  had  been  eaten 
through  the  metal ;  b  is  a  socket  which  had  been  short  cir- 
cuited, and  the  excessive  damage  was  due  to  overfusing  ot 
circuit. 

At  c  and  e,  the  effects  of  electrolysis  on  wire  are  shown ; 
c  is  a  piece  of  underwriter's  wire  (not  approved  in  moulding), 
which  had  been  used  in  damp  moulding,  the  leak  to  ground 
through  the  dampness  causing  the  gradual  eating. away  of  the 
wire;  c  shows  a  breakdown  in  the  insulation  and  subsequent 
electrolytic  action  on  the  wire,  causing  it  finally  to  break. 
This  wire  had  been  used  in  a  round-house,  where  the  sulphur 
fumes  and  the  condensation  of  escaping  steam  on  insulators 
had  formed  a  path  to  ground.  At  d  is  an  incandescent  lamp 
which  had  been  covered  with  a  towel,  the  confined  heat  soft- 
ening the  glass  and  setting  fire  to  the  towel.  The  danger  of 
fire  from  overheated  lamps  is  much  greater  than  is  generally 
supposed.  Small  lamps  and  lamps  subject  to  a  little  excess 
of  voltage  are  especially  dangerous,  and  many  instances  are 
on  record  where  they  have  charred  woodwork  and  set  fire 
to  cloth  or  paper  shades. 

It  may  in  many  cases  seem  unnecessary  to  have  bushings 
in  one  piece  long  enough  to  pass  through  a  floor,  or  wide 
wall;  but  especially  in  passing  through  floors,  it  is  very  easily 
possible  for  wires  to  become  crossed  between  the  joists;  that 
is,  the  wire  entering  at  the  right  above  the  floor  may  be 


INSIDE   WORK. 


101 


brought  out  at  the  left  below  the  floor  and  the  other  wire 
through  the  opposite  holes.  In  such  a  case  the  two  wires  of 
opposite  polarity  will  be  in  contact,  and  should  the  insulation 
give  out  from  any  cause  whatever,  such  as  abrasion,  or  the 
gnawing  of  rats  and  mice,  there  would  be  nothing  to  prevent 
a  short  circuit  and  consequent  fire.  In  passing  through  floors 
or  walls  the  wires  often  come  in  contact  with  concealed  pipes 
or  other  grounded  material,  so  that  only  by  making  the  bush- 
ings continuous  can  the  wires  be  properly  protected. 

Figure  48  shows  short  bushings  arranged  in  iron  pipe. 
Figure  49  shows  a  case  where  there  is  an  offset  in  the  wall. 
Cases  of  this  kind  very  often  occur.  Sometimes  the  floor  can 
be  taken  up  and  an  iron  conduit,  properly  bent,  put  in  place ;  or 
the  wires  placed  on  insulators.  In  this  latter  case  the  floor 
must  not  be  put  down  until  the  inspector  has  examined  the 
wires.  The  wires  may  be  run  on  top  of  the  floor  to  such  a 
place  where  a  continuous  bushing  may  be  dropped  through 


Figure  47  Figure  48  Figure  49 

the  floor.  The  wires  on  top  of  the  floor  must  be  then  pro- 
tected by  a  suitable  boxing  or  at  least  the  same  dimensions  as 
given  for  boxing  on  side  walls. 

e.     Must  be  kept  free  from  contact  with  gas,  water  or  other 
metallic  piping,  or  any  other  conductors  or  conducting  ma- 


102 


MODERN   ELECTRICAL  CONSTRUCTION. 


terial  which  they  may  cross,  by  some  continuous  and  firmly 
fixed  non-conductor,  creating  a  separation  of  at  least  one  inch. 
Deviations  from  this  rule  may  sometimes  be  allowed  by  spe- 
cial permission. 

When  one  wire  crosses  another  wire  the  best  and  usual 
means  of  separating  them  is  by  means  of  a  porcelain  tube  on 
one  of  them.  The  tube  should  be  prevented  from  moving  out 
of  place,  either  by  a  cleat  at  each  end,  or  by  taping  it  securely 
to  the  wire. 

The  same  method  may  be  adopted  where  wires  pass  close 
to  iron  pipes,  beams,  etc.,  or,  where  the  wires  are  above  the 
pipes,  as  is  generally  the  case,  ample  protection  can  frequently 
be  secured  by  supporting  the  wires  well  with  a  porcelain  cleat 
placed  as  nearly  above  the  pipe  as  possible. 

Figure  50  is  a  sectional  view  of  the  manner  in  which  wires 
are  usually  run  through  joists  in  bushings.  For  small  wires 
bushings  should  preferably  be  installed  as  shown  at  top ;  never 
as  shown  in  the  middle  row.  For  larger  wires  the  holes  must 


Figure  50 

be  bored  as  straight  as  possible ;  otherwise  it  will  be  difficult 
to  pull  wires  through.  The  quantity  of  wire  needed  is  also 
somewhat  increased  by  slanting  the  holes.  In  open  places 
wires  are  generally  installed  on  insulators  as  shown  in  Fig- 
ure 51. 

Figure  51  shows  different  methods  employed  where  one 
wire  crosses  another.  The  method  at  the  left,  which  is  more 
suited  to  large  stiff  wires,  does  not  quite  comply  with  the  rule, 
but  is  very  often  used.  The  other  two  methods  are  preferable. 
Insulating  supports  should  always  be  provided  at  the  place 
of  crossing  to  prevent  the  upper  wires  from  sagging  and 
resting  on  the  lower;  also  to  prevent  any  strain  from  coming 
on  tap  joints.  Approved  flexible  tubing  such  as  circular  loom 


IXSIDE    WORK. 


103 


is  also  often  used  in  crossing  wires  and  pipes.  In  dry  loca- 
tions it  is  quite  safe  and  does  not  break  as  easily  as  tubes, 
but  should  never  be  used  where  there  is  any  likelihood  of 
dampness. 

f.     Must  be  so  placed  in  wet  places  that  an  air  space  will 
be   left  between   conductors  and  pipes   in   crossing,   and   the 


Figure  51 


former  must  be  run  in  such  a  way  that  they  cannot  come  in 
contact  with  the  pipe  accidentally.  Wires  should  be  run  over 
rather  than  under  pipes  upon  which  moisture  is  likely  to 
gather  or  which,  by  leaking,  might  cause  trouble  on  a  circuit. 

This  is  a  rule  that  is  very  often  violated,  as  much  work  is 
done  using  loom,  as  shown  at  the  left  of  Figure  52,  and  is 
quite  safe  with  gas  pipes.  With  cold  water  pipes,  which  are 


Figure  52 

likely  to  sweat,  or  with  steam  pipes,  it  is  very  bad  practice. 
Where  pipes  are  close  against  a  ceiling  it  is  better  either  to 
fish  over  them  or  drop  wires  some  distance  below  them  as 


104  MODERN   ELECTRICAL   CONSTRUCTION. 

illustrated  at  the  right  of  the  figure.  No  part  of  the  wiring 
should  be  in  contact  with  pipes.  On  side  walls  where  ver- 
tical wires  run  across  horizontal  pipes  the  only  safeguard 
would  be  to  box  the  pipes  and  run  the  moisture  to  one  side. 
The  most  harm  is  done  by  water  on  the  insulators.  If  these 
can  be  kept  dry  it  does  not  matter  much  about  wires  which 
hang  free  in  the  air.  Whatever  form  of  insulation  is  used 
in  crossing  pipes,  it  must  be  continuous.  Short  bushings 
strung  on  the  wire,  where  a  large  pipe  or  number  of  pipes 
are  being  crossed,  is  not  satisfactory,  as  the  bushings  are 
apt  to  separate  or  moisture  gather  in  the  space  between  them. 
The  insulation  must  also  be  firmly  attached  to  the  wires.  If 
knobs  are  not  used  as  shown  in  Figure  51  to  keep  the  bush- 
ings in  place,  they  must  be  taped  to  the  wire. 

g.  The  installation  of  electrical  conductors  in  wooden 
moulding  or  where  supported  on  insulators  in  elevator  shafts 
will  not  be  approved,  but  conductors  may  be  installed  in  such 
shafts  if  encased  in  approved  metal  conduits. 

Wires  supported  on  insulators  in  such  places  are  very  likely 
to  be  disturbed,  especially  in  freight  elevators.  Moulding  is 
often  so  impregnated  with  oil,  and  the  draft  in  an  elevator 
shaft  is  usually  so  strong  that  a  blaze  once  started  would 
quickly  run  to  the  top. 

15.    Underground  Conductors. 

a.  Must   be    protected    against    moisture    and    mechanical 
injury   where   brought    into   a   building,    and    all   combustible 
material  must  be  kept  from  the  immediate  vicinity. 

b.  Must   not  be    so   arranged   as   to    shunt    the   current 
through  a  building  around  any  catch-box. 

By  reference  to  Figure  53  the  meaning  of  this  rule  will 
be  made  clear.  With  wires  run  as  shown  it  would  be  easy 
for  any  one  having  disconnected  one  service  switch  to  believe 
all  wires  in  the  building  dead,  while  they  were  in  reality  still 
being  kept  alive  by  the  other  switch. 


INSIDE   WORK. 


105 


c.  Where    underground    service    enters    building    through 
tubes,  the  tubes  shall  be  tightly  closed  at  outlets  with  asphalt- 
urn  or  other  non-conductor,   to  prevent  gases  from   entering 
the  building  through  such  channels. 

d.  No  underground  service  from  a  subway  to  a  building 
shall  supply  more  than  one  building  except  by  written  permis- 
sion from  the  Inspection  Department  having  jurisdiction. 

17.     Switches,  Cut-Outs,  Circuit-Breakers,  Etc. 

(For  construction  rules  sec  Nos.  51,  52  and  53.) 

a.  Must,  unless  otherwise  provided  (for  exceptions,  see 
No.  8  c  and  No.  22  c),  be  so  arranged  that  the  cut-outs  will 
protect,  and  the  opening  of  a  switch  or  circuit-breaker  will 


\ 


_ 


^   I       i   fiS** 

Figure  53 

disconnect,  all  of  the  wires ;  that  is,  in  a  two-wire  system  the 
two  wires,  and  in  a  three-wire  system  the  three  wires,  must  be 
protected  by  the  cut-out  and  disconnected  by  the  operation  of 
the  switch  or  circuit  breaker. 

The  exceptions  are  in  regard  to  motors  of  l/4  H.  P.  or 
less  on  circuits  of  not  over  300  volts  and  incandescent  cir- 
cuits of  not  over  660  watts  where  single  pole  switches  are 
allowed.  This  rule  forbids  the  practice,  as  sometimes  em- 


106 


MODERN   ELECTRICAL   CONSTRUCTION. 


ployed  on  switchboards,  of  breaking  the  two  outside  wires  of 
a  3-wire  system  and  leaving  the  neutral,  which  is  not  carried 
through  the  switch,  always  connected.  •  .  . 

In  connecting  double-pole  snap  switches  the  wireman 
should  be  very  careful.  Most  of  these  switches  cross  polari- 
ties as  shown  in  Figure  54,  and  if  connected  wrong  will  form 
short  circuits.  Many  of  them  have  been  connected  that  way, 
even  by  wiremen  of  some  experience. 

b.  Must  not  be  placed  in  the  immediate  vicinity  of  easily 
ignitable  stuff  or  where  exposed  to  inflammable  gases  or  dust 
or  to  flyings  of  combustible  material. 

In  starch  and  candy  factories,  grain  elevators,  flouring 
mills,  and  buildings  used  for  woodworking  or  other  purposes 
which  would  cause  the  fittings  to  be  exposed  to  dust  and  flyings 
of  inflammable  material,  the  cut-outs  and  switches  should  be 
placed  in  approved  cabinets  outside  of  the  dust-rooms.  If, 
however,  it  is  necessary  to  locate  them  in  the  dust-rooms,  the 
cabinets  must  be  dust-proof  and  must  be  provided  with  self- 
closing  doors. 

Whenever  an  electric  current  is  broken,  whether  by  fuse 
or  switch,  an  arc  varying  with  the  current  strength,  is 


Figure  54 


Figure  55 


Figure  56 


formed.  Should  a  switch  be  only  partly  opened,  this  arc 
will  continue  and  consume  the  metal  of  the  switch  until  the 
gap  in  which  it  burns  becomes  too  long,  when  the  current 
will  be  broken.  Meanwhile  there  is  much  heat  generated 


INSIDE   WORK.  107 

which  may  readily  communicate  to  inflammable  material 
nearby. 

There  seems  to  be  no  reason  except  economy  of  wire  why 
cut-outs  should  ever  be  placed  inside  of  dust  rooms.  Switches 
of  course  must  often  be  placed  in  such  rooms  as  in  many 
cases  the  entire  building  outside  of  the  engine  room  is  dusty. 
In  such  cases  the  switches  as  well  as  the  cutouts  may,  how- 
ever, be  often  placed  on  the  outside  walls  convenient  to  some 
window. 

An  approved  cabinet  is  shown  in  Figure  55.  If  used  in 
connection  with  knife  switches  it  should  be  large  enough  to 
admit  being  closed  when  the  switch  is  open.  In  cases  where 
cut-outs  and  switches  must  be  located  in  dusty  rooms,  it 
would  be  well  to  construct  double  cabinets,  one  part  for  the 
cut-outs  and  another  for  the  switches.  The  fuses,  which  are 
the  most  dangerous  can  then  be  tightly  enclosed,  as  it  will 
seldom  be  necessary  to  get  at  them.  In  practice  it  has  been 
found  almost  impossible  to  keep  the  doors  of  cabinets  which 
are  much  used  closed.  It  seems  next  to  impossible  to  con- 
struct a  cabinet  which  is  dust  proof,  with  a  door  that  can  be 
readily  opened,  and  a  self-closing  door  can  hardly  be  made 
to  remain  dustproof.  Doors  are  made  self-closing  either 
through  gravity  or  by  suitable  springs. 

As  switch  and  cut-out  boxes  are  very  likely  to  be  used  for 
the  storage  of  cotton  waste,  paper,  etc.,  which  would  readily 
ignite  from  a  melted  fuse,  it  would  be  well  to  construct  them 
with  a  slanting  bottom  as  indicated  by  the  dotted  line  in  Fig- 
ure 56,  so  that  nothing  will  lie  in  them. 

c.  Must,  when  exposed  to  dampness,  either  be  enclosed 
in  a  waterproof  box  or  mounted  on  porcelain  knobs. 

Figure  56  is  a  sectional  side  view  of  a  cut-out  box  for  use 
out  of  doors.  In  it  the  switch  is  mounted  on  porcelain  knobs. 
In  all  damp  places  much  trouble  is  experienced  from  leakage 
through  the  moisture  on  the  surface  of  the  slate  or  marble 


108  MODERN   ELECTRICAL  CONSTRUCTION. 

and  through  the  wax  used  to  cover  the  bare  parts  on  back  of 
switch. 

d.  Time  switches  must  be  enclosed  in  an  iron  box  or 
cabinet  lined  with  fire  resisting  material. 

If  an  iron  box  is  used,  the  minimum  thickness  of  the  iron 
must  be  0.128  cf  an  inch  (No.  8  B.  &  S.  Gauge). 

If  the  cabinet  is  used,  it  must  be  lined  with  marble  or 
slate  at  least  %  of  an  inch  thick,  or  with  iron  not  less  than 
0.128  of  an  inch  thick.  Box  or  cabinet  must  be  so  constructed 
that  when  switch  operates  blade  shall  clear  the  door  by  at 
least  one  inch. 


CONSTANT-CURRENT  SYSTEMS. 

PRINCIPALLY  SERIES  ARC  LIGHTING. 

18.     Wires. 

(Sec  also  Nos.  14,  15  and  16.) 

a.  Must  have  an  approved  rubber  insulating  covering  (see 
No.  41). 

b.  Must  be   arranged   to   enter   and    leave    the    building 
through  an  approved  double-contact  service  switch    (see  No. 
51  &),  mounted  in  a  non-combustible  case,  kept  free  from  mois- 
ture, and  easy  of  access  to  police  or  firemen. 

In  order  that  all  of  the   wiring  in  the  building  may  be 
entirely  disconnected  a  switch,  the  principle  of  which  is  illus- 


Figure  57 

trated  at  d,  Figure  57,  is  provided  where  wires  enter  and 
leave  the  building.  A  modern  commercial  form  of  this  switch 
is  shown  in  Figure  58.  This  switch  never  breaks  the  circuit. 
As  shown  in  Figure  57,  the  current  passes  from  the  positive 
pole,  through  the  upper  blade  of  the  switch  to  b  and  thence 


CONSTANT  CURRENT   SYSTEMS. 


109 


through  the  arc  lamps  back  to  c  and  to  the  negative  pole. 
When  it  is  desired  to  extinguish  the  lamps  the  two  blades  of 
the  switch  are  moved  downward,  as  indicated  by  the  dotted 
lines.  The  contacts  d  are  arranged  so  that  both  switch  blades 
connect  with  them  before  disconnecting  entirely  from  the 
points  b  and  c.  As  soon  as  both  blades  are  in  contact  with  d 
all  current  flows  through  it  because  the  resistance  of  it  is 
so  very  much  less  than  that  of  the  lamps.  With  the  switch  in 
the  position  indicated  by  dotted  lines,  the  current  still  flows 
in  the  outside  wires,  but  all  wires  within  the  building  are 
"dead."  At  c,  Figure  57,  is  shown  a  single-pole  switch  which 
operates  on  the  same  principle  as  the  other.  If  this  switch  is 
closed  all  current  will  pass  through  it  ;  if  open  the  current  will 
pass  through  the  last 
lamp.  A  switch  of  this 
kind  is  always  arranged 
within  the  lamp  itself. 
This  latter  way  of 
switching  lamps  should 
never'  be  used,  as  a  lamp 
switched  in  this  way  is 
never  safe  to  handle. 
There  is  just  as  much 
danger  from  shocks 
when  the  lamp  is 
switched  off  as  when  on. 
With  switches  as  de- 
scribed above  there  is  no 

spark  whatever  when  lamps  are  switched  off,  but  there  is  usu- 
ally quite  a  spark  when  the  lamps  are  switched  in.  Should  there 
be  a  broken  wire  or  a  lamp  out  of  order  in  the  circuit  to  be 
switched  in,  there  will  be  quite  an  arc  maintained  for  some 
time.  In  such  a  case  the  switch  should  be  quickly  closed  and 
the  trouble  located. 


Fig.  58. 


110  MODERN   ELECTRICAL  CONSTRUCTION. 

In  handling  live  wires  of  this  system  great  care  is  neces- 
sary. The  wireman  should  insulate  himself  from  the  ground 
by  a  dry  board,  or,  if  all  about  him  is  damp,  by  a  board  resting 
on  insulators.  Rubber  gloves  and  rubber  boots,  if  kept  dry, 
are  useful. 

Death  or  bad  burns  may  result  if  the  wireman,  standing  on 
wet  ground  or  any  conductor  in  connection  with  it,  touches 
part  of  a  circuit  which  is  also  partly  in  connection  with  the 
ground.  If,  in  Figure  57,  the  wire  at  /  is  grounded,  a  man  in 
connection  with  the  ground  and  touching  a  bare  wire  at  h  will 
receive  a  shock  due  to  about  50  volts,  but  if  he  touches  the 
wire  at  g,  he  will  receive  a  shock  of  about  150  volts.  The 
shock  received  from  a  line  containing  100  lamps  may  be  any- 
thing from  50  to  5,000  volts,  and  may  result  in  only  a  slight 
burn  or  in  instant  death. 

Another  danger  in  connection  with  live  circuits  is  the  lia- 
bility of  cutting  oneself  into  circuit.  If  one  is  perfectly 
insulated  from  the  ground  there  is  no  harm  whatever  in  touch- 
ing one  live  wire  (with  very  high  voltages  such  insulation  is, 
however,  hard  to  obtain)  with  either  one  or  both  hands  while 
the  wires  are  in  order.  Should,  however,  the  wire  between 
the  two  hands  break,  the  current  would  immediately  pass 
through  the  body,  very  likely  causing  instant  death.  Even  if 
the  circuit  is  not  entirely  broken,  if  only  a  resistance  is  cut  in, 
the  shock  will  be  very  severe.  As,  for  instance,  if  one  should 
touch  the  terminal  of  an  arc  lamp,  not  burning,  with  each  hand 
nothing  whatever  would  be  felt,  but,  if  the  lamp  were  now 
suddenly  switched  on,  there  would  be  a  very  severe  shock  at 
first,  which  would  become  less  so  when  the  lamps  were  fairly 
started.  To  avoid  the  possibility  of  such  occurrences  when 
working  on  live  lamps  or  circuits  a  short  wire  known  as  a 
"jumper"  is  often  connected,  as  at  k,  Figure  57.  This  will 
carry  all  current,  and  there  is  now  no  danger  except  from  a 
connection  to  ground. 


CONSTANT  CURRENT   SYSTEMS.  Ill 

c.  Must  always  be  in  plain  sight,  and  never  encased,  except 
when   required   by   the    Inspection   Department  having  juris- 
diction. 

What  is  known  as  concealed  knob  and  tube  work  is  not 
allowed  in  wiring  for  H.  T.  arcs ;  neither  can  the  wires  be 
run  in  moulding  or  conduit. 

It  has  been  customary  to  use  no  smaller  than  No.  6  wire 
for  these  high  tension  series  circuits.  The  current  required 
is  seldom  more  than  10  amperes,  and  No.  14  wire  has  sufficient 
carrying  capacity,  but  its  mechanical  strength  is  not  very 
great.  The  danger  from  a  broken  wire  in  high  tension  sys- 
tems is  much  greater  than  in  low  tension  systems,  because  of 
the  long  arc  which  occurs  at  the  break.  The  loss  in  volts  per 
100  feet  with  No.  6  will  be  about  .4,  while  with  No.  14  it  will 
be  2.6.  This,  however,  will  not  affect  the  lights,  because  the 
pressure  at  the  machine  must  be  correspondingly  increased. 

d.  Must   be    supported    on    glass    or   porcelain    insulators, 
which  separate  the  wire  at  least  one  inch  from  the  surface 
wired  over,  and  must  be  kept  rigidly  at  least  eight  inches  from 
each  other,  except  within  the  structure  of  lamps,  on  hanger- 
boards  or  in  cut-out  boxes,  or  like  places,  where  a  less  distance 
is  necessary. 

An  extra  precaution  often  taken  in  this  kind  of  work  on 
plastered  walls  is  ta  place  a  wooden  block  or  rosette  about  three 
inches  in  diameter  and  one-half  inch  thick  under  each  insu- 
lator ;  this  secures  greater  separation  from  ceilings  and  side 
walls  and  adds  greatly  to  the  stability  of  the  insulators.  On 
plastered  walls  a  small  insulator,  if  subjected  to  side  strain, 
will  cut  into  the  plaster  on  one  side  and  allow  the  wires  to  sag, 
the  wooden  block  will  prevent  this. 

e.  Must,  on  side  wall,  be  protected  from  mechrnical  injury 
by  a  substantial   boxing,   retaining  an   air  space  of  one  inch 
around  the  conductors,  closed  at  the  top    (the  wires  passing 
through   bushed   holes),   and   extending   not   less   than   seven 
feet  from  the  floor.     When  crossing  floor  timbers  in  cellars, 
or  in  rooms  where  they  might  be  exposed  to  injury,  wires 


112 


MODERN   ELECTRICAL   CONSTRUCTION. 


must  be  attached  by  their  insulating  supports  to  the  under 
side  of  a  wooden  strip  not  less  than  one-half  an  inch  in  thick- 
ness. Instead  of  the  running-boards,  guard  strips  on  each 
side  of  and  close  to  the  wires  will  be  accepted.  These  strips 
to  be  not  less  than  seven-eighths  of  an  inch  in  thickness  and 
at  least  as  high  as  the  insulators. 

Except  on  joisted  ceilings,  a  strip  one-half  of  an  inch 
thick  is  not  considered  sufficently  stiff  and  strong.  For  spans 
of  say  eight  or  ten  feet,  where  there  is  but  little  vibration, 
one-inch  stock  is  generally  sufficiently  stiff;  but  where  the 
span  is  longer  than  this  or  there  is  considerable  vibration, 
still  heavier  stock  should  be  used. 

For  general  suggestions  as  to  protecting  wires  on  side 
walls,  see  notes  under  No.  24  e. 

Figure  59  is  an  illustration  of  protection  on  side  walls, 
giving  the  dimensions  required.  The  wooden  block  shown, 
which  raises  bushings  above  floor,  is  an  extra  protection  to 

.k 


Figure  59 

prevent  water  from  running  into  them.  The  iron  pipe  is 
shown  extending  in  one  piece  clear  through  the  floor.  With 
voltages  used  in  this  system  a  separate  pipe  should  be  pro- 
vided for  each  wire,  unless  alternating  currents  are  used. 


CONSTANT  CURRENT  SYSTEMS.  llo 

19.     Series  Arc  Lamps. 

(For  construction  rules,  see  No.  57.) 

a.  Must  be  carefully  isolated  from  inflammable, material. 

b.  Must  be  provided  at  all  times  with  a  glass  globe  sur- 
rounding the  arc,  and  securely  fastened  upon  a  closed  base. 
Broken  or  cracked  globes  must  not  be  used. 

c.  Must  be  provided  with  a  wire  netting  (having  a  mesh 
not  exceeding  one  and  one-fourth  inches)    around  the  globe, 
and  an  approved  spark  arrester   (see  No.  58),  when  readily 
inflammable  material  is  in  the  vicinity  of  the  lamps,  to  prevent 
escape  of  sparks  of  carbon  or  melted  copper.     It   is   recom- 
mended   that    plain    carbons,   not   copper-plated,    be   used    for 
lamps  in  such  places. 

Outside  arc  lamps  must  be  suspended  at  least  eight  feet 
above  sidewalks.  Inside  arc  lamps  must  be  placed  out  of 
reach  or  suitably  protected. 

Arc  lamps,  when  used  in  places  where  they  are  exposed  to 
flyings  of  easily  inflammable  material,  should  have  the  car- 
bons enclosed  completely  in  a  tight  globe  in  such  manner  as 
to  avoid  the  necessity  for  spark  arresters. 

"Enclosed  arc"  lamps,  having  tight  inner  globes,  may  be 
used,  and  the  requfrements  of  Sections  b  and  c  above  would 
of  course,  not  apply  to  them,  except  that  a  wire  netting 
around  the  inner  globe  may  in  some  cases  be  required  if  the 
outer  globe  is  omitted. 

d.  Where  hanger-boards  (see  No.  56)  are  not  used,  lamps 
must  be  hung  from  insulating  supports  other  than  their  con- 
ductors. 

At  the  left,  Figure  60  is  shown,  the  usual  method  of  sus- 
pending outdoor  arc  lamps  on  buildings.  The  supporting  wire 
may  be  fastened  to  brick  or  stone  walls  by  drilling  a  hole  about 
four  inches  deep  and  plugging  this  securely  with  wood,  when 
an  eye  or  lag  bolt  or  large  spike  may  be  driven  or  screwed  into 
it.  Expansion  bolts,  of  which  there  are  many  kinds  to  be  had, 
may  also  be  used.  It  is  best  to  arrange  the  supporting  wires 
at  quite  a  high  angle,  otherwise  the  direct  outward  pull  may 
be  too  great.  Some  of  the  older  arc  lamps  are  not  provided 
with  insulators,  and  may  be  suspended,  as  shown  in  the  center 
of  the  figure.  On  very  low  ceilings,  lamps  are  often  arranged 


114  MODERN   ELECTRICAL   CONSTRUCTION. 

as  shown  at  the  right,  the  plastering  being  cut  away  and  lamp 
suspended  from  floor  above  joists.    The  space  above  plaster 


Figure  60 

must  be  enclosed   on   all   sides  and   all   v;oodwork  protected 
with  asbestos  board  at  least  one-eighth  inch  thick. 

If  this  method  is  used  with  constant  potential  arc  lamps 
carrying  resistance  in  the  hood,  it  would  be  well  to  remove 
or  short-circuit  this  resistance  and  locate  another  in  a  more 
suitable  place. 

20.  Incandescent  Lamps  in  Series  Circuits. 

a.  Must  have  the  conductors  installed  as  required  in  No. 
18,  and  each  lamp  must  be  provided  with  an  automatic  cut-out. 

b.  Must  have  each  lamp  suspended  from  a  hanger-board 
by  means  of  rigid  tube. 

c.  No  electro-magnetic  device  for  switches  and  no  mul- 
tiple-series   or    series-multiple    system    of    lighting    will    be 
approved. 

d.  Must  not  under  any  circumstances  be  attached  to  gas 
fixtures. 

CONSTANT-POTENTIAL  SYSTEMS. 

GENERAL  RULES — ALL  VOLTAGES. 

21.  Automatic  Cut-Outs   (Fuses  and  Circuit-Breakers). 

(Sec  No.  17,  and  for  construction,  Nos.  52  and  53.) 
Excepting  on  main  switchboards,  or  where  otherwise  sub- 


CONSTANT  POTENTIAL   SYSTEMS.  115 

ject    to    expert    supervision,    circuit-breakers    will   not   be   ac- 
cepted unless  fuses  are  also  provided. 

The  cut-out  is  the.  principal  protective  device  used  in  elec- 
tric light  and  power  work.  In  its  simplest  form  it  consists  of 
a  piece  of  wire  made^  of  a  certain  alloy  designed  to  melt  at 
a  comparatively  low  temperature  and  so  connected  that  all 
current  used  in  a  certain  circuit  must  pass  through  it.  We 
have  already  seen  that  currents  of  electricity  generate  heat  in 
the  conductors  through  which  they  pass,  and  that  this  heat 
is  proportional  to  the  square  of  the  current  flowing;  that  is, 
if  we  double  the  current  we  shall  increase  the  production  of 
heat  fourfold.  A  dangerous  rise  in  current  strength  may 
be  due  to  a  "short  circuit'  or  to  an  overload,  too  many  lamps 
or  motors  being  connected  to  a  circuit.  To  prevent  damage 
to  wires  and  other  apparatus  from  excessive  currents,  fuses 
or  cut-outs  must  be  installed.  When  the  current  rises  above 
its  allowed  strength  the  fuse  melts  and  opens  the  circuit; 
that  is,  stops  all  current  flow.  This  melting  of  the  fuse  is 
always  accompanied  by  a  flash  of  fire,  called  an  arc,  and 
may  easily  set  fire  to  inflammable  material  located  near  the 
fuses.  In  the  case  of  large  fuses  pieces  of  molten  lead  are 
often  spattered  about. 

Another  device  used  for  the  same  purpose  as  the  fuse 
or  cut-out  is  known  as  the  circuit-breaker.  A  circuit-breaker 
in  its  simplest  form  comprises  a  knife  switch  which  when 
closed  is  forced  in  against  a  spring  and  held  in  place  by 
means  of  a  small  catch.  A  solenoid,  inside  of  which  is  placed 
a  moveable  iron  core,  is  connected  in  series  with  one  side  of 
the  switch.  When  the  current  passing  through  this  solenoid 
exceeds  a  certain  amount,  the  iron  core  is  drawn  up  into  it, 
and,  striking  against  the  catch,  releases  the  switch  which  will 
then  fly  open,  thus  cutting  off  the  current.  The  core  of  this 
solenoid  is  so  designed  that  when  it  starts  to  move  its  speed 
is  greatly  accelerated  so  that  it  strikes  the  catch  a  sharp 


116  MODERN   ELECTRICAL   CONSTRUCTION. 

blow.  By  means  of  a  small  adjusting  screw  the  circuit  break- 
er can  be  set  to  operate  at  various  current  strengths  within 
its  limits.  For  this  reason  and  for  the  further  reason  that 
it  is  so  easily  made  inoperative  by  tying  or  blocking  its  sol- 
enoid it  is  not  approved  for  general  use  unless  fuses  are  also 
installed.  It  may  be  used  under  the  care  of  a  competent  elec- 
trician who  understands  the  dangers  of  its  abuse. 

a.  Must  be  placed  on   all   service  wires,  either  overhead 
or  underground,  as  near  as  possible  to  the  point  where  they 
enter  the  building  and  inside  the  walls,  and  arranged  to  cut 
off  the  entire  current  from  the  building. 

Where  the  switch  required  by  No.  22  is  inside  the  build- 
ing, the  cut-out  required  by  this  section  must  be  placed  so 
as  to  protect  it. 

In  risks  having  private  plants,  the  yard  wires  running 
from  building  to  building  are  not  generally  considered  as  ser- 
vice wires,  so  that  cut-outs  would  not  be  required  where  the 
wires  enter  buildings,  provided  that  the  next  fuse  back  is 
small  enough  to  properly  protect  the  wires  inside  the  building 
in  question. 

The  fuse  block  here  required  serves  a  double  purpose;  it 
affords  protection  to  the  whole  installation  while  in  use,  and 
is  an  effective  means  of  disconnecting  a  building  when  cur- 
rent is  no  longer  used.  This  can  also  be  accomplished  by 
means  of  the  service  switch,  but  a  switch 
is  so  easily  closed  by  anyone  that  it  must 
never  be  relied  upon  entirely  for  this 
purpose. 

Figure  61  shows  arrangement  of  fuses 
and  switch  as  commonly  installed  where 
wires  enter  buildings.  The  wires  enter  at 
the  top,  connect  to  the  fuse  terminals,  cur- 
rent passing  through  the  fuses  to  the 
switch. 

b.  Must    be    placed    at    every    point          Fig.  61. 


CONSTANT   POTENTIAL   SYSTEMS.  117, 

where  a  change  is  male  in  the  size  of  wire  [unless  the  cut- 
out in  the  larger  wire  will  protect  the  smaller  (see  No.  61)]. 

Figure  62,  A  to  D,  shews  systems  of  distribution  and  ar- 
rangement of  mains  in  ger.eral  use.  Figure  A  shows  the 
simplest  and  cheapest  method  ^f  running  mains,  and  is 
known  as  the  "tree  system."  Beginning  at  the  service  the 
wires  must  be  large  enough  to  carry  the  whole  current  to  the 
first  floor  or  wherever  the  first  cut-out  center  is  located. 
At  this  point  the  size  of  wire  may  be  reduced  because  it  will 
be  required  to  carry  only  the  current  used  further  on.  Main 
cut-outs  should  be  arranged  as  shown  in  the  figure  at  1 
and  2.  That  is,  the  cut-outs  protecting  the  mains  must  be  in- 
stalled in  the  mains  at  each  floor  after  the  current  for  that 
floor  has  been  taken  off.  Cases  are  often  found  where  the 
cut-out  is  placed  in  the  main  line  ahead  of  the  branch  blocks. 
This  is  obviot'.sly  wrong,  as  the  fuse  will  have  to  be  too  heavy 
to  protect  the  smaller  mains. 

Figure  B  shows  a  somewhat  different  arrangement  which 
requires  more  wire  and  is  more  expensive  in  the  beginning, 
but  far  more  satisfactory  and  economical  in  operation.  With 
the  wires  arranged  as  shown  in  the  diagram  the  pressure  at 
all  the  lamps  will  be  nearly  uniform.  Even  if  the  mains 
are  designed  for  a  considerable  loss  to  the  center  of  dis- 
tribution the  dynamo  may  be  made  to  compensate  for  this 
loss  and  keep  the  lamps  burning  properly.  With  the  tree 
system,  A,  this  is  impossible ;  the  lamps  at  the  first  cut-out 
center  will  either  be  too  bright  or  those  at  the  last  center 
too  dim. 

Figure  C  shows  a  convertible  three-wire  system.  Three- 
wire  circuits  may  also  be  run  as  shown  in  Figures  A  and  B, 
using  three  instead  of  two  wires. 

In  order  to  convert  a  three-wire  system  into  a  two-wire 
system  the  two  outside  wires  are  joined  together.  The  mid- 
dle wire  then  forms  or.e  side  of  the  system  and  the  outside 


118 


MODERN    ELECTRICAL  CONSTRUCTION. 


Figure  62 


CONSTANT   POTENTIAL   SYSTEMS.  119 

wires  the  other.  The  middle  wire  must  carry  as  much  cur- 
rent as  both  outside  wires  combined  and  should  have  a  carry- 
ing capacity  equal  to  them.  It  should  be  remembered  that  a 
wire  containing  simply  twice  as  many  circular  mils  does  not 
fulfil  this  requirement  as  is  shown  in  the  table  on  page  — 
which  must  be  consulted  in  selecting  wires. 

In  three-wire  systems  the  middle  or  neutral  wire  is  merely 
a  balancing  wire  and  normally  carries  very  little  or  no  current, 
but  it  is  very  important  that  it  remain  intact.  If  for  instance 
in  Figure  D  the  branch  circuit  a  has  twelve  lights  burning 
while  there  are  also  12  lights  burning  on  b,  the  current  will 
pass  from  the  positive  wire  through  the  lower  fuse  to  a, 
through  the  twelve  lights  in  a  back  to  the  middle  fuse,  thence 
through  the  12  lights  in  b  to  the  upper  fuse  and  negative  wire, 
the  two  sets  of  lamps  burning  in  series.  If  now  the  lamps  in 
b  are  switched  off  the  current  from  a  can  no  longer  pass 
through  them  and  instead  returns  through  the  middle  fuse  to 
the  neutral  wire.  If  only  six  lights  in  b  are  burning,  while 
12  are  burning  in  a,  the  current  of  6  lights  will  return  over  the 
negative  wire  and  the  other  six  in  a  will  return  over  the 
neutral  wire.  Should  the  neutral  wire  be  broken  or  its  fuse 
blown  there  would  be  no  return  path  on  it  for  the  extra  cur- 
rent, and  consequently  the  current  passing  through  the  twelve 
lights  in  a  would  be  forced  through  the  six  lights  in  b.  caus- 
ing them  to  burn  with  excessive  brilliancy  and  to  break  in  a 
very  short  time.  Should  a  short  circuit  occur,  say  on  circuit 
b,  with  the  neutral  wire  intact,  it  would  merely  blow  a  fuse, 
but  if  the  main  neutral  fuse  were  out  it  would  bring  220  volts 
on  circuit  a  and  speedily  cause  damage  to  the  lamps.  Thus 
it  will  be  seen  that  it  is  of  great  importance  to  fuse  the  neu- 
tral wire  so  that  it  will  not  easily  blow  out.  The  cut-out 
shown  in  Figure  D  is  not  approved  because  it  does  not  pro- 
vide independent  double  fused  branch  circuits.  The  style  of 
wiring  shown  in  connection  with  it  was  formerly  much  in 
vcr"c  bvt  is  net  now  much  used. 


120 


MODERN   ELECTRICAL   CONSTRUCTION. 


Figure  C  shows  a  system  of  wiring  quite  often  used.  A 
set  of  heavy  mains  are  run  from  the  service  or  dynamo  to  the 
top  floor  and  taps  taken  off  at  each  floor.  These  mains  do 
not  change  size  at  each  fleer,  but  are  continuous  for  their  en- 
tire length.  While  this  method  has  some  of  the  objections  of 
the  tree  system  in  regards  to  voltage,  still  the  faults  of  the 
tree  system  are  greatly  reduced  to  the  much  smaller  losses 
in  the  mains  between  the  upper  floors  or  those  farthest  from 
the  dynamo. 

Figure  63  shows  the  method  of  fusing  main  switch  and 
branch  circuits.  The  switch  itself  will  require  a  fuse  to  pro- 
tect it  although  it  need  not  be  right  at  the  switch. 

It  often  becomes  necessary  to  reinforce  a  set  of  mains, 
especially  for  motors  which  have  become  overloaded,  by  run- 
ning another  wire  in  parallel  with  the  old  as  indicated  in 
Figures  64  and  65.  Two  separate  and  distinct  ways  of  ar- 


Fig.  63  Fig.  64       Fig.  65  Fig.  66 

ranging  them  are  shown  and  it  depends  upon  the  conditions 
as  to  which  is  preferable.  If  the  wires  are  small  or  run  in 
places  where  they  are  liable  to  be  broken,  the  plan  shown  in 
Figure  64  is  the  better.  Here  each  wire  is  properly  fused  and 
if  one  breaks  the  other  carries  the  whole  load  until  its  fuse 


CONSTANT   POTENTIAL   SYSTEMS.  121 

melts.  If  the  wires,  as  often  happens,  are  much  overfused, 
the  breaking  of  one  wire  would  force  the  other  to  carry 
the  whole  current  and  become  overheated.  If  the  arrange- 
ment were  as  in  Figure  65  the  unbroken  wire  would  carry  the 
current  indefinitely  and  soon  become  overheated.  On  the 
other  hand,  if  both  wires  are  large  and  the  run  is  short  the 
fuses  arranged  as  in  Figure  64  may,  through  poor  contacts, 
prevent  one  or  the  other  of  the  wires  from  obtaining  its 
full  share  of  the  current.  The  fuse  making  poor  contact 
would  force  a  much  greater  share  of  current  through  the 
other  wire.  In  most  cases  the  better  plan  would  be  to  ar- 
range the  wires  as  in  Figure  65.  If  the  current  supplied  is 
for  lights  the  branch  cut-outs  can  be  separated  and  each  set 
of  mains  allowed  to  supply  a  certain  part  of  them,  when 
each  set  should  be  made  independent.  For  sizes  of  wires  to 
be  used  for  reinforcing,  see  Tables. 

With  the  three-wire  system  where  a  larger  motor  load 
and  a  few  lights  are  run  the  lights  are  often  fused  as  shown 
in  Figure  66,  a  small  wire  being  run  for  the  neutral,  this 
smaller  wire,  of  course,  being  properly  fused  at  the  main  cut- 
out. Plug  cut-outs  of  the  type  shown  in  this  figure  often 
have  the  metal  parts  projecting  above  the  porcelain ;  they 
should  be  connected  so  that  the  metal  parts  which  project  are 
dead  when  the  plugs  are  removed.  This  will  prevent  many 
short  circuits  on  disconnected  cut-outs. 

Figure  67  shows  the  method  of  converting  a  two-wire 
system  into  a  three-wire  system  with  one  extra  wire  to  run. 
This  extra  wire  will  very  likely  not  need  to  be  as  large  as  the 
other  wires  are,  because  the  three-wire  system  requires  only 
one-half  as  much  current  and  it  should,  therefore,  be  used  as 
the  neutral.  This  arrangement  will  secure  the  full  benefit  of 
all  the  copper  in  the  old  wires  (which  are  probably  much  larger 
than  necessary)  and  will  operate  at  a  very  small  loss. 

Figure  68  shows  a  straight  three-wire  system  changed  to 


122 


MODERN   ELECTRICAL  CONSTRUCTION. 


a  two-wire  system,  one  extra  wire  run  for  it.  If  the  three 
wires  are  of  the  proper  capacity  the  addition  of  the  fourth 
wire  as  in  the  figure  will  make  it  correct  for  two-wire  sys- 


Figure  67 


Figure 


Figure  69 


terns,  the  mains  feeding  the  upper  and  lower  groups  being,  of 
course,  properly  fused  where  they  start. 

In  Figure  69  the  cut-outs  are  so  connected  that  all  branch 
wires  leaving  the  cut-out  box  at  either  side  are  of  the  same 
polarity.  This  is  often  useful  where  many  wires  are  to  be  run 
close  together. 

c.  Must  be  in  plain  sight,  or  enclosed  in  an  approved 
cabinet  (see  No.  54),  and  readily  accessible.  They  must  not 
be  placed  in  the  canopies  or  shells  of  fixtures. 

The  ordinary  porcelain  link  fuse  cut-out  will  not  be  ap- 
proved. Link  fuses  may  be  used  only  when  mounted  on  slate 
or  marble  bases  conforming  to  No.  52  and  must  be  enclosed 
in  dust-tight,  flreproofed  cabinets,  except  on  switchboards 
located  well  away  from  combustible  material,  as  in  the  ordi- 
nary engine  and  dynamo  room  and  where  these  conditions  will 
be  maintained. 


CONSTANT  POTENTIAL  SYSTEMS.  123 

While  it  is  required  that  cut-out  cabinets  be  accessible  there 
is  also  danger  in  making  them  too  accessible,  for  such  cabi- 
nets are  very  often  used  for  storage  of  paper  or  cotton  waste. 
It  would  seem  that  about  eight  feet  above  the  floor  is  the 
most  desirable  height  to  place  them  or  the  cabinet  may  be 
arranged  with  a  slanting  bottom  which  will  make  it  impossible 
to  store  anything  in  it.  It  is  also  well  to  arrange  the  cut-out 
cabinet  away  from  inflammable  material,  for  long  experience 
has  shown  that  doors  are  nearly  always  left  open.  Especially 
is  this  the  case  when  switches  are  in  the  same  cabinets  with 
the  cut-outs. 

d.  Must  be  so  placed  that  no  set  of  incandescent  lamps 
requiring  more  than  660  watts,  whether  grouped  on  one  fixture 
or  on  several  fixtures  or  pendants,  will  be  dependent  upon  one 
cut-out.  Special  permission  may  be  given  in  writing  by  the 
Inspection  Department  having  jurisdiction  for  departure  from 
this  rule  in  the  case  of  large  chandeliers,  stage  borders  and 
illuminated  signs. 

The  above  rule  shall  also  apply  to  motors  ,when  more 
than  one  is  dependent  on  a  single  cut-out. 

The  idea  is  to  have  a  small  fuse  to  protect  the  lamp 
socket  and  the  small  wire  used  for  fixtures,  pendants,  etc. 
It  also  lessens  the  chances  of  extinguishing  a  large  number 
of  lights  if  a  short  circuit  occurs. 

"On  open  work  in  large  mills  approved  link  fused  ro- 
settes may  be  used  at  a  voltage  of  not  over  125  and  approved 
enclosed  fused  rosettes  at  a  voltage  of  not  over  250,  the  fuse 
in  the  rosettes  not  to  exceed  3  amperes,  and  a  fuse  of  over  25 
amperes  must  not  be  used  in  the  branch  circuit." 

All  branches  or  "taps"  from  a  three-wire  Edison  system 
must  be  run  as  two-wire  circuits. 

c.  The  rated  capacity  of  fuses  must  not  exceed  the  allow- 
able carrying  capacity  of  the  wire  as  given  in  No.  16.  Circuit- 
breakers  must  not  be  set  more  than  30  per  cent  above  the  al- 
lowable carrying  capacity  of  the  wire,  unless  a  fusible  cut-out 
is  also  installed  in  the  circuit. 

A  16  c.  p.  incandescent  lamp  is  usually  estimated  at  55 
watts  and  consequently  the  number  of  lamps  allowed  on  one 
circuit  is  usually  twelve,  whether  110  or  220  volts  are  used. 


124  MODERN   ELECTRICAL  CONSTRUCTION. 

If  voltages  lower  than  110  are  us.  I  the  current  required  by 
twelve  55  watts  lamps  will  be  too  great,  and  fewer  lamps 
should  be  used  per  circuit.  Although  a  number  of  small  fan 
motors  may  be  run  on  one  circuit  each  motor  should  be  pro- 
vided with  a  switch  ;  as  a  rule  such  a  switch  is  on  the  motor. 

22.    Switches. 

(Sec  No.  17,  and  for  construction,  No  51). 

a.  Must  be  placed  on  all  service  wires,  either  overhead  or 
underground,  in  a  readily  accessible  place,  as  near  as  possible 
to  the  point  where  the  wires  enter  the  building  and  arranged 
to  cut  off  the  entire  current. 

Service  cut-out  and   switch  must  be  arranged  to  cut  off 
current  from  all  devices  Including  meters. 


In    risks    having   private    plants    the   yard    wires    running 
building  are  not  generally  considered  as  ser- 
vice  wires,    so    that    switches    would    not   be    required    in   each 


from  building  to  building  are  not 


, 

building   if   there   are   other   switches   conveniently   located   on 
the  mains  or  if  the  generators  are  near  at  hand. 

In  overhead  construction  the  best  plan  is  to  locate  the 
switch  at  either  front  or  rear  of  building  so  that  wires  may 
lead  to  it  direct  from  pole.  Avoid  running  wires  on  sides  of 
building  where  it  is  likely  that  other  buildings  may  be  erected. 
In  underground  construction,  where  the  space  under  sidewalk 
and  basement  is  not  occupied,  it  is  advisable  to  place  a  cut-out 
where  wires  enter  the  building  from  street  and  to  locate  the 
service  switch  in  a  more  accessible  place. 

Although  the  rules  do  not  call  for  switch  to  be  installed  in 
each  separate  building  in  the  case  of  large  plants,  still  it  is 
often  advisable  to  install  them,  for  in  case  of  trouble  it  is  nec- 
essary that  the  current  can  be  immediately  shut  off.  A  switch 
is  also  useful  in  cases  of  trouble  on  the  wiring,  to  allow  of 
repairing. 

b.  Must  always  be  placed  in  dry,  accessible  places,  and  be 
grouped  as  far  as  possible.  Knife  switches  must  be  so  placed 
that  gravity  will  tend  to  open  rather  than  close  them. 


CONSTANT   POTENTIAL   SYSTEMS. 


125 


"When  possible,  switches  should  be  so  wired  that  l/.ades 
will  be  "dead"  when  switch  is  open. 

If  knife  switches  are  used  in  rooms  where  combustible 
flyings  would,  be  likely  to  accumulate  around  them,  they 
should  be  enclosed  in  dust-tight  cabinets.  (See  note  under 
No.  17  b.)  Even  in  rooms  where  there  are  no  combustiblo 
materials  it  is  better  to  put  all  knife  switches  in  cabinets,  in 
order  to  lessen  the  danger  of  accidental  short  circuits  being 
made  across  their  exposed  metal  parts  by  careless  workmen. 

Up  to  250  volts  and  thirty  amperes,  approved  indicating 
snap  switches  are  advised  in  preference  to  knife  switches 
on  lighting  circuits  abcut  the  workrooms. 

To  comply  with  this  rule  will  ordinarily  bring  the  fuses 
of  knife  switches  directly  under  the  handle  of  switch.  If  there 
happens  to  be  a  short  circuit  0:1  the  \vires  when  switch  is  closed 
the  fuses  will  blow  instantly  and  very  li'.iely  burn  the  operator's 
hand.  In  connection  with  such  switches  cartridge  fuses  should 
be  used  or  the  switches,  especially  the  larger  ones,  closed  by 


O  II 

Figure  70  Figure  71 

pushing  them   in  with  a  stick.     The  danger  from  opening  a 
switch  is  much  less. 

Figure  70  shows  a  switch  arranged  to  comply  with  all  three 
points  of  this  rule,  the  feed  wires  coming  from  bebw.  This 
requires  that  incoming  and  outgoing  wires  pass  e-ach  other. 
In  this  case,  the  wires  pass  each  other  behind  the  switch  base, 


126  MODERN   ELECTRICAL  CONSTRUCTION. 

they  being  encased  in  flexible  tubing.  A  side  view  is  also  given 
in  Figure  71.  Instead  of  passing  behind  the  switch  the  wires 
may,  of  course,  run  around  one  side  to  the  top,  the  other  wires 
around  the  other  side  to  the  bottom. 

Figure  71  illustrates  a  cabinet  so  arranged  that  the  switch 
within  can  be  opened  or  closed  without  opening  the  cabinet. 
The  cover  Is  hinged  at  the  top,  and  slotted  in  the  center,  which 
leaves  room  for  the  lever  by  which  the  switch  is  worked  to 
adjust  itself  so  it  will  always  be  out  of  the  way.  A  switch 
which  is  often  used  may  as  well  be  left  without  a  cover  as  with 
one,  for  the  door  must  be  opened  or  closed  every  time  the 
switch  is  used,  and  the  cabinet  will  always  be  found  open. 
Figure  71  will  answer  where  only  protection  against  acci- 
dental contacts  is  required. 

c.  Must  not  be  single  pole  when  the  circuits  which  they 
control  supply  devices  which  require  over  660  watts  of  energy, 
or  when  the  difference  of  potential  is  over  300  volts. 

This  rule  allows  the  use  of  single  pole  switches  on  circuits 
of  660  watts,  6  amperes  at  110  vots,  or  3  amperes  at  220  volts, 
which  corresponds  roughly  to  twelve  16  cp.  lamps.  In  systems 
that  are  not  grounded  a  single  pole  switch  will  answer  fairly 


Figure  72 


well  if  large  enough.  It  will  readily  open  the  circuit  and  it 
offers  no  opportunities  for  short  circuits,  as  do  double  pole 
switches.  Where,  however,  three  wire  systems  with  grounded 
neutrals  are  used  double-pole  switches  are  preferable,  for  by 
reference  to  Figure  72  one  can  readily  see  that  if  the  neutral 


CONSTANT   POTENTIAL   SYSTEMS.  127 

or  middle  wire  is  grounded  (which  is  equivalent  to  being  in 
connection  with  gas  piping)  and  another  ground  should  come 
on  to  the  wiring  say  at  a,  the  single-pole  switch,  S,  would 
not  control  the  lights  at  all.  The  current  would  flow  from  the 
positive  wire  to  the  top  fuse,  through  the  twelve  lights  to 
ground  a,  through  the  ground  to  the  neutral  or  middle  wire 
and  back  to  the  dynamo,  regardless  of  whether  the  switch  is 
on  or  off.  Also,  a  man  working  at  the  lights  could  easily 
make  a  short-circuit  by  bringing  the  wires  into  contact  with 
the  gas  piping  even  if  the  switch  were  turned  off.  When 
single-pole  switches  are  used  in  connection  with  such  circuits 
they  should  never  be  placed  in  the  neutral  wire  as  in  the  dia- 
gram. If  the  switch  S  were  placed  in  the  top  wire  these 
troubles  would  be  avoided.  Often  times,  however,  switches 
are  connected  before  the  circuits  are  run  into  cut-outs  and  an 
attempt  to  place  single-pole  switches  on  a  certain  wire  requires 
considerable  care,  which  many  wiremen  will  not  take.  In  the 
case  of  only  two  wires  from  a  central,  three-wire,  station  being 
run  into  a  building,  the  neutral  wire  is  not  known  until  meters 
are  set  and  instructions  would,  therefore,  have  to  be  left  for 
meter  men  which  would  often  be  disregarded,  so  that  in  all 
cases  on  three-wire  grounded  systems  double-pole  switches  are 
preferable. 

d.  Where   flush   switches  are  used,   whether  with   conduit 
systems  or  not,  the  switches  must  be  enclosed  in  boxes  con- 
structed  of  iron   or   steel.     No  push   buttons   for  bells,   gas- 
lighting  circuits,  or  the  like  shall  be  placed  in  the  same  wall 
plate  with  switches  controlling  electric  light  or  power  wiring. 

This    requires  an   approved  box   in   addition   to   the  porce- 
lain enclosure  of  the  switch. 

e.  Where  possible,  at  all  switch  or  fixture  outlets,  a  %-mch 
block  must  be  fastened  between  studs  or  floor  timbers  flush 
with  the  back  of  lathing  to  hold  tubes,  and  to  support  switches 
or  fixtures.     When  this  cannot  be  done,  wooden  base  blocks, 
not  less  than  24-inch  in  thickness,  securely  screwed  to  lathing, 


128 


MODERN   ELECTRICAL   CONSTRUCTION. 


must  be  provided  for  switches,  and  also  for  fixtures  which  are 
not  attached  to  gas  pipes  or  conduit  tubing. 

Figure  73  shows  concealed  wiring  back  of  lathing  leading 
to  a  double-pole  flush  switch.  The  board  fastened  between 
studdings  must  be  cut  out  to  admit  the  box  of  switch  and  the 


II 


Figure  73 


Figure  74 


size  of  this  box  should  be  known  when  wires  are  put  in.  The 
board  should  not  rest  hard  against  the  lathing,  but  leave  a 
little  space  for  plaster  to  work  in  behind  the  lath.  Loom  is  put 
on  all  wires  at  outlets  and  must  extend  back  to  the  nearest 
knob. 

Figure  74  shows  two  methods  of  fastening  snap  switches 
by  means  of  wooden  blocks  first  fastened  to  the  plaster.  One 
block  is  cut  out  so  as  to  bring  all  wires  under  the  switch  and 
entirely  conceal  them.  The  opening  in  block  to  admit  wires 
and  bushings  should  be  oblong,  so  as  to  leave  room  on  two 
sides  for  the  screws  with  which  the  switch  is  to  be  fastened. 
On  the  other  block  the  wires  and  bushing  are  brought  through 
close  to  the  outer  edge  of  switch  base.  By  careful  workman- 
ship a  neat  job  can  be  done  in  this  way.  As  most  snap 
switches  cross  conductors,  that  is,  connect  points  a  and  b,  if 


CONSTANT   POTENTIAL   SYSTEMS. 


129 


from  the  nature  of  the  case  it  becomes  necessary  to  run  any  of 
the  wires  close  together  these  two  wires  may.be  run  that  way, 
for  they  can  never  be  of  opposite  polarity. 

23.  Electric  Heaters. 

a.  Must  be  placed  in  a  safe  situation,  isolated  from  inflam- 
mable materials,  and  be  treated  as  sources  of  heat. 

b.  Must    each    have    a    cut-out    and    an    indicating    switch 
(see  No.  17  a). 

,r.  The  attachments  of  feed  wires  to  the  heaters  must  be  in 
plain  sight,  easily  accessible,  and  protected  from  interference, 
accidental  or  otherwise. 

d.  The  flexible  conductors  for  portable  apparatus,  such  as 
irons,  etc.,   must  have  an  approved   insulating  covering    (see 
No.  45  g). 

e.  Must    each    be    provided    with    name-plate,    giving   the 
maker's  name  and  the  normal  capacity  in  volts  and  amperes. 


Figure  75 


Stationary  heaters  should  be  treated  like  stoves  which 
might  become  overheated  at  any  time. 

Portable  heaters,  such  as  flat  irons,  have  this  danger,  that 
if  left  standing  with  the  current  on  they  in  time  accumulate 
heat  enough  to  char  combustible  material  and  to  finally  set 
it  on  flre. 

It  is  often  desirable  to  connect  in  multiple  with  the  heat- 
ers, an  incandescent  lamp  of  low  candle  power,  as  it  shows 
at  a  glance  whether  or  not  the  switch  is  open,  and  tends  to 
prevent  its  being  left  closed  through  oversight. 


130  MODERN   ELECTRICAL   CONSTRUCTION. 

In  Figure  75  is  given  a  diagram  of  a  heater  circuit  with  a 
4  cp.  lamp  in  circuit.  Where  there  are  many  irons  in  use,  as  in 
some  tailoring  establishments,  it  is  advisable  to  run  them  all 
from  one  set  of  mains  with  a  main  switch  convenient  to  exit 
door  and  have  this  switch  opened  whenever  the  irons  are  not 
in  use.  The  individual  switch  at  each  iron  should  be  located 
as  near  as  possible  to  each  iron.  Cords  feeding  irons  or  cloth 
cutting  machines  are  often  installed  as  shown,  insulators  are 
strung  on  a  tight  wire  and  the  cord  tied  to  them.  This  allows 
considerable  latitude  in  moving  the  iron. 


LOW  POTENTIAL  SYSTEMS. 


131 


Low-Potential   Systems. 

550  VOLTS  OR  LESS. 

Any  circuit  attached  to  any  machine,  or  combination  of  ma- 
chines, which  develops  a  difference  of  potential  between 
any  two  wires,  of  over  ten  volts  and  less  than  550  volts, 
shall  be  considered  as  a  low-potential  circuit,  and  as  com- 
ing under  this  class,  unless  an  approved  transforming  de- 
vice is  used,  which  cuts  the  difference  of  potential  doivn  to 
ten  volts  or  less.  The  primary  circuit  not  to  exceed  a 
potential  of  3,500  volts. 

Before  Pressure  is  raised  above  300  volts  on  any  previously 
existing1  system  of  wiring-,  the  whole  must  be  strictly  brought 
up  to  all  of  the  requirements  of  the  rules  at  date. 

24.     Wires. 

GENERAL   RULES. 

(Sec  also  Nos.  14,  15  and  16.) 

a.  Must  be  so  arrang-ed  that  under  no  circumstances  will 
there  be  a  difference  of  potential  of  over  300  volts  between  any 
bare  metal  parts  in  any  distributing-  switch  or  cut-out  cabinet, 
or  equivalent  center  of  distribution. 

This  rule,  as  far  as  it  applies  to  pressures  higher  than  300 
volts,  contemplates  a  3-wire  system  on  which,  instead  of  the 


-2tO  -•  1-220— ' 


Figure  76 

customary  110  volts  on  each  side  of  the  neutral,  220  volts  are 
used,  making  a  pressure  of  440  volts  between  the  two  outside 
wires. 


132 


MODERN  ELECTRICAL  CONSTRUCTION. 


The  ordinary  110-220  volt,  3-wire  system  will  require  to  be 
changed  at  cut-out  centers  as  shown  in  Figure  76,  where  it 
will  be  seen  a  difference  of  potential  greater  than  220  volts  can- 
not be  found  within  any  cut-out  box,  or  at  any  switch  or  cut- 
out. 

Special  attention  should  be  given  to  the  balancing  of  the 
load  with  this  arrangement  of  wiring  and  both  sides  of  the 
system  should  be  brought  into  every  room  or  hall  requiring 


Figure  77 

more  than  one  circuit.  False  ideas  of  economy  should  not 
induce  one  to  arrange  large  groups  of  lamps  on  one  side  of 
the  system  in  order  to  save  a  few  cut-out  boxes. 

6.     Must  not  be  laid  in  plaster,  cement,  or  similar  finish, 
and  must  never  be  fastened  with  staples. 


LOW   POTENTIAL   SYSTEMS.  133 

c.  Must  not  be  fished  for  any  great  distance,  and  only  in 
places  where  the  inspector  can  satisfy  himself  that  the  rules 
have  been  complied  with. 

Figure  77  illustrates  a  very  common  combination  of  "fish" 
and  "moulding"  work.  Moulding  is  used  to  bring  the  wires 
from  the  floor  to  the  ceiling  and  along  the  ceiling  to  a  point 
opposite  the  outlet  and  parallel  with  the  joists.  From  this 
point  to  the  fixture  the  wires  can  then  be  readily  fished. 

The  connection  between  the  fish  and  moulding  work  should 
be  made  as  shown  at  the  right,  where  ihe  moulding  is  cut  out 
so  as  to  admit  the  loom.  It  is  better,  even,  to  have  the  loom 
show  to  some  extent  than  to  have  the  wire  come  in  contact 
with  the  plaster,  as  will  very  likely  be  the  case  if  the  loom  is 
not  fully  brought  through. 

d.  Twin  wires  must  never  be  used,  except  in  conduits,  or 
where  flexible  conductors  are  necessary. 

Flexible  conductors  are  in  general  considered  necessary 
only  with  pendant  sockets,  certain  styles  of  adjustable  brack- 
ets, portable  lamps,  motors  and  stage  plugs,  or  heating  ap- 
paratus. 

e.  Must  be  protected  on  side  walls  from  mechanical  injury- 
When  crossing  floor  timbers  in  cellars,  or  in  rooms  where  they 
might  be  exposed  to  injury,  wires  must  be  attached  by  their 
insulating  supports  to  the  under  side  of  a  wooden  strip,  not 
less  than  one-half  inch  in  thickness,  and  not  less  than  three 
inches  in  width.  Instead  of  the  running  boards,  guard  strips 
on  each  side  of  and  close  to  the  wires  will  be  accepted.  These 
strips  to  be  not  less  than  seven-eighths  of  an  inch  in  thickness, 
and  at  least  as  high  as  the  insulators. 

Suitable  protection  on  side  walls  may  be  secured  by  a  sub- 
stantial boxing,  retaining  an  air  space  of  one  inch  around  the 
conductors,  closed  at  the  top  (the  wires  passing  through  bushed 
holes),  and  extending  not  less  than  five  feet  from  the  floor;  or 
by  an  iron-armored  or  metal-sheathed  insulating  conduit  suf- 
ficiently strong  to  withstand  the  strain  to  which  it  will  be  sub- 
jected, and  with  the  ends  protected  by  the  lining  or  by  special 
insulating  bushings,  so  as  to  prevent  the  possibility  of  cutting 


134 


MODERN   ELECTRICAL  CONSTRUCTION. 


the  wire  insulation;  or  by  plain  metal  pipe,  lined  with  approved 
flexible  tubing,  which  must  extend  from  the  nsulator  next 
below  the  pipe  to  the  one  next  above  it. 

If  metal  conduits  or  iron  pipes  are  used  to  protect  wires  car- 
rying alternating  currents,  the  two  or  more  wires  of  each  cir- 
cuit must  be  placed  in  the  same  conduit,  as  troublesome  induc- 
tion effects  and  heating  of  the  pipe  might  otherwise  result;  and 
the  insulation  of  each  wire  must  be  reinforced  by  approved  flex- 
ible tubing  extending  from  the  insulator  next  below  the  pipe  to 
the  one  next  above  it  This  should  also  be  done  in  direct-cur- 
rent wiring  if  there  is  any  possibility  of  alternating  current 
ever  being  used  on  the  system. 

For  high-voltage  work,  or  in  damp  places,  the  wooden  boxing 
may  be  preferable,  because  of  the  precautions  which  would  be 
necessary  to  secure  proper  insulation  if  the  pipe  were  used. 
With  these  exceptions,  however,  iron  pipe  is  considered  prefer- 
able to  the  wooden  boxing,  and  its  use  is  strongly  urged.  It 
is  especially  suitable  for  the  protection  of  wires  near  belts,  pul- 
leys, etc. 

f.  When  run  in  unfinished  attics,  or  in  proximity  to  water 
tanks  or  pipes,  will  be  considered  as  exposed  to  moisture. 


Figure  78 


Figure  78  illustrates  the  meaning  of  the  rule  in  regard  to 
wires  run  along  low  ceilings. 

Figure  79  gives  the  dimensions  necessary  for  boxing  wires 
on  side  walls.  At  the  right,  the  sidewall  protection  consists 
of  conduit;  a  junction  box  with  the  lower  side  knocked  out  is 
used  to  enclose  bushings.  When  the  cover  is  screwed  on  the 
wires  are  completely  enclosed. 


LOW   POTENTIAL   SYSTEMS. 


135 


SPECIAL  RULES. 

For  Open  Work. 

In  dry  places. 

g.  Must  have  an  approved  rubber  or  "slow-burning  weath- 
erproof" insulation  (see  Nos.  41  and  42.) 

A  "slow-burning  weatherproof"  covering  is  considered  good 
enough  where  the  wires  are  entirely  on  insulating  supports. 
Its  main  object  is  to  prevent  the  copper  conductors  from  com- 
ing accidentally  into  contact  with  each  other  or  anything  else. 

Most  of  this  wire  as  it  is  now  made  with  the  weather-proof 
braid  on  the  outside,  becomes  sticky  when  exposed  to  the  tern- 


Figure  79 


perature  found  in  most  mill  rooms  in  summer.  This  is  objec- 
tionable, especially  in  linty  places,  as  dust  and  flyings  readily 
adhere  to  the  wires,  making  it  difficult  to  keep  them  clear. 
Under  these  conditions,  the  "sweeping-down"  process  generally 
results  in  loosening  and  deranging  the  wires  in  a  short  time. 
The  weatherproof  insulation  is  also  very  combustible,  and 


136 


MODERN   ELECTRICAL  CONSTRUCTION. 


when  on  the  outside  might  allow  fire  to  spread  along  the  wires, 
especially  if  there  were  a  number  of  wires  near  together,  as 
stated  in  the  note  to  No  2  b  For  these  reasons  it  is  considered 
preferable  to  place  the  weatherproof  insulation  next  to  the  con- 
ductor, and  the  slow-burning  braids  on  the  outside.  The  outer 
surface  should  then  be  finished  hard  and  smooth,  similar  to 
that  on  the  old  so-called  "underwriter"  wire  A  wire  insulated 
in  this  manner  is  not  open  to  the  objections  noted  above,  and 
can  also  be  more  readily  drawn  into  flexible  tubing  where  the 
iron  pipe  construction  described  in  the  note  to  Section  e  is  used. 
h.  Must  be  rigidly  supported  on  non-combustible,  non- 
absorptive  insulators,  which  will  separate  the  wires  from  each 
other  and  from  the  surface  wired  over  in  accordance  with  the 
following  table  : 

Voltage.  Distance  from  Distance  between 

Surface.  Wires. 


0  to  300 
301  to  550 


%inch 
1      Inch 


2%  inch 
4      inch 


Rigid  supporting  requires  under  ordirfary  conditions,  where 
wiring  along  flat  surfaces,  supports  at  least  every  four  and 
one-half  feet.  If  the  wires  are  liable  to  be  disturbed,  the  dis- 
tance between  supports  should  be  shortened.  In  buildings  of 
mill  construction,  mains  of  No.  8  B.  &  S.  gage  wire  or  over, 
where  not  liable  to  be  disturbed,  may  be  separated  about  six 
inches,  and  run  from  timber  to  timber,  not  breaking  around, 
and  may  be  supported  at  each  timber  only. 

This  rule  will  not  be  interpreted  to  forbid  the  placing  of  the 
neutral  of  an  Edison  three-wire  system  in  the  center  of  a  three- 
wire  cleat  where  the  difference  of  potential  between  the  outside 
wires  is  not  over  300  volts,  provided  the  outside  wires  are  sep- 
arated two  and  one-half  inches. 

Figure  80  shows  different  methods  of  running  wires  in 
buildings  of  mill  construction.  If  the  method  shown  at  a  is 


Figure  80 

used,  a  few  insulators  should  be  placed  here  and  there  and  the 
wires  tied  to  them  to  prevent  sagging.  The  arrangements 
shown  at  b  and  c  are  suitable  for  small  wires  on  high  ceilings. 


LOW   POTENTIAL   SYSTEMS.  137 

The  methods  shown  at  d  and  c  are  sometimes  used  where 
there  is  no  danger  of  interference.  With  long  spans,  supports 
as  shown  at  f  may  be  used. 

In  damp  places,  or  buildings  specially  subject  to  moisture  or 
to  acid  or  other  fumes  liable  to  injure  the  wires  or  their 
insulation. 

i.     Must  have  an  approved  insulating  covering. 

For  protection  against  water,  rubber  insulation  must  be 
used.  For  protection  against  corrosive  vapors,  either  weath- 
erproof or  rubber  insulation  must  be  used  (See  Nos  41  and  44.) 

j.  Must  be  rigidly  supported  on  non-combustible,  non-ab- 
sorptive insulators,  which  separate  the  wire  at  least  one  inch 
from  the  surface  wired  over,  and  must  be  kept  apart  at  least 
two  and  one-half  inches  for  voltages  up  to  300,  and  four  inches 
for  higher  voltages. 

Rigid  supporting  requires  under  ordinary  conditions,  where 
wiring  over  flat  surfaces,  supports  at  least  every  four  and  one- 
half  feet.  If  the  wires  are  liable  to  be  disturbed,  the  distance 
between  supports  should  be  shortened.  In  buildings  of  mill 
construction,  mains  of  No.  8  B.  &  S.  gage  wire  or  over,  where 
not  liable  to  be  disturbed,  may  be  separated  about  six  inches, 
and  run  from  timber  to  timber,  not  breaking  around,  and  may 
be  supported  at  each  timber  only. 

k.     (Stricken  out.) 

In  damp  places  the  wires  are  often  run  on  the  under  side 
of  an  inverted  trough  as  shown  in  Figure  81.  The  main  point 
of  usefulness  of  such  a  trough  lies  in  the  fact  that  it  prevents 
drippings  from  wetting  the  wires  and  insulators.  Condensa- 
tion will,  however,  keep  insulators  and  wires  wet  nevertheless. 

The  trough,  to  be  useful,  should  be  put  together  with  many 
screws,  the  butting  edges  of  the  boards  having  been  first 
painted  with  a  waterproof  paint,  with  which,  when  finished,  the 
whole  trough  is  also  painted  inside  and  out. 

Notwithstanding  the  rule  given  above,  it  would  seem  far 
better  where  practicable  to  use  petticoat  insulators  and  keep 
them  much  farther  apart,  even,  if  in  order  to  do  so  a  larger 
wire  would  be  required.  Each  insulator,  when  wet,  allows 
some  current  to  leak  over  its  surface  and,  therefore,  the 


138 


MODERN   ELECTRICAL  CONSTRUCTION. 


fewer  we  have  the  better  so  long  as  there  is  no  danger  of  break- 
ing wires.  If  splices  are  necessary  in  wet  places  they  should 
be  made  quite  a  distance  from  insulators;  the  insulation  of  a 
splice  being  always  weaker  than  that  of  the  unbroken  wire. 
Care  should  also  be  taken  that  the  insulation  of  wires  is  not 
damaged  through  tying. 

Weather  proof  sockets  are  required  by  the  rule  and  are 


Figure  81 

best  in  such  places  when  not  subject  to  much  handling.  As 
these  are,  however,  easily  broken,  brass  shell  sockets  are  often 
used.  These  are  thoroughly  covered  with  tape  and  compound 
so  as  to  exclude  all  moisture  and  are  very  durable. 

For  Moulding  Work. 

/.  Must  have  an  approved  rubber  insulating  covering  (see 
No.  41). 

m.  Must  never  be  placed  in  moulding  in  concealed  or 
damp  places,  or  where  the  difference  of  potential  between  any 
two  wires  in  the  same  moulding  is  over  300  volts. 

As  a  rule,  moulding  should  not  be  placed  directly  against 
a  brick  wall,  as  the  wall  is  likely  to  "sweat"  and  thus  introduce 
moisture  back  of  the  moulding. 

Figure  82  shows  the  dimensions  of  approved  moulding. 
Figure  83  shows  the  proper  method  of  making  a  tap  joint 


LOW   POTENTIAL   SYSTEMS. 


139 


in  moulding.  This  method  brings  the  capping  between  the  two 
wires  of  opposite  polarity.  Wires  should  never  be  crossed  be- 
low the  capping.  If  the  exposed  wire  in  Figure  83  is  objec- 
tionable, part  of  the  back  of  moulding  may  be  cut  out,  or  the 


Figure  82 


Figure  83 

wall  back  of  the  moulding  may  be  gouged  out  as  shown  in  Fig- 
ure S4.  This  method  must,  however,  never  be  used  with  other 
than  walls  or  partitions  of  hardwood. 

Figure  85  shows  proper  method  of  tapping  flexible  cord  to 


Fig.  84  Figure  85 

wires  in  moulding.  The  whole  cord  should  never  be  taken 
out  of  one  hole  in  capping.  There  is  always  some  chance  of 
abrasion  and  joints  are  often  poorly  covered,  so  that  there  is 
always  mere  likelihood  cf  ?hort  circuits  at  this  point. 


140 


MODERN   ELECTRICAL  CONSTRUCTION. 


Figure  86  shows  how  moulding  should  be  fastened  to  tile 
ceiling.  When  toggle  bolts  are  used,  the  nut  should  always  be 
put  on  outside  of  capping  (unless  a  very  small  one  is  used,  or 


Figure  87  Figure  88 

more  than  ordinary  care  is  exercised).  Many  wiremen  are 
careless  and  cut  away  the  middle  tongue  too  much,  giving  the 
nut  a  chance  to  work  itself  diagonally  across  it,  so  as  to  come 
in  contact  with  both  wires  and,  in  time  perhaps,  cause  short 
circuits.  Although  toggle  bolts  are  mostly  used,  screws  have 
been  successfully  used  in  tile.  It  is  only  necessary  to  first 
drill  a  hole  of  just  the  proper  size  for  the  screw  to  be  used. 

A  very  rough,  quick  way  of  making  a  square  turn  with 
moulding  is  shown  in  Figure  87.  One  piece  is  cut  entirely 
off  along  the  line  a;  the  pieces  are  then  joined  as  shown  and 


Figure 

the  capping  hides  the  botch  work.  Such  work  will  not  be 
passed  by  inspectors  if  noticed.  The  proper  way  of  fitting 
moulding  is  shown  in  Figure  88. 


LOW   POTENTIAL   SYSTEMS.  141 

Figure  89  shows  methods  of  running  round  corners.  The 
saw  cuts,  a,  b,  c,  etc.,  should  be  made  with  a  fine  saw  and  for 
short  bends  require  to  be  close  together.  Bending  is  facilitated 
by  wetting  the  moulding  ar.d  if,  before  the  moulding  is  put  in 
place,  the  saw  cuts  are  filled  with  glue,  it  will  greatly  add  to 
the  durability  of  the  job.  Screws  or  nails  used  in  fastening 
the  capping  should  pass  through  the  moulding  into  the  wall  to 
get  a  firm  hold. 

For  Conduit  Work. 

n.  Must  have  an  approved  rubber  insulating  covering 
(see  No.  47). 

o.  Must  not  be  drawn  in  until  all  mechanical  work  on  the 
building  has  been,  as  far  as  possible,  completed. 

p.  Must,  for  alternating  systems,  have  the  two  or  more 
wires  of  a  circuit  drawn  in  the  same  conduit. 

It  is  advised  that  this  be  done  for  direct-current  systems 
also,  so  that  they  may  be  changed  to  alternating  systems  at  any 
time,  induction  troubles  preventing  such  a  change  if  the  wires 
are  in  separate  conduits. 

"The  same  conduit  must  never  contain  circuits  of  different 
systems,  but  may  contain  two  or  more  circuits  of  the  same 
system." 

If  a  single  wire  carrying  alternating  currents  of  electricity 
were  run  in  iron  pipe,  there  would  be  a  very  large  drop  in 
voltage.  This  drop  is  due  to  the  fact  that  all  currents  while 
changing  in  strength  generate  a  counter  E.  M.  F.  in  their  sur- 
roundings. This  is  particularly  strong  when  the  wires  are  sur- 
rounded by,  or  very  close  to,  iron.  If  both  wires  are  run  in 
the  same  pipe,  the  current  in  one  wire  neutralizes  that  of  the 
other  and  there  is  no  trouble. 

For  Concealed  "Knob  and  Tube"  Work. 

q.  Must  have  an  approved  rubber  insulating  covering  (see 
No.  41). 

r.     Must  be  rigidly  supported  on  non-combustible,  non-ab- 


142 


MODERN   ELECTRICAL  CONSTRUCTION. 


sorptive  insulators  which  separate  the  wire  at  least  one  inch 
from  the  surface  wired  over.  Must  be  kept  at  least  ten  inches 
apart,  and,  when  possible,  should  be  run  singly  on  separate 
timbers  or  studdings.  Must  be  separated  from  contact  with 
the  walls,  floor  timbers  and  partitions  through  which  they  may 
pass  by  non-combustible,  non-absorptive  insulating  tubes,  such 
as  glass  or  porcelain. 

Rigid  supporting:  requires  under  ordinary  conditions,  where 
wiring  along  flat  surfaces,  supports  at  least  every  four  and  one- 
half  feet.  If  the  wires  are  liable  to  be  disturbed,  the  distance 
between  supports  should  be  shortened. 

s.    "When,  in  a  concealed  knob  and  tube  system,  it  is  im- 


practicable to  place  any  circuit  on  non-combustible  supports 
of  glass  or  porcelain,  approved  metal  conduit,  or  approved 
armored  cable  must  be  used  (see  No.  24  f)  except  that  if  the 
difference  of  potential  between  the  wires  is  not  over  300  volts, 
and  if  the  wires  are  not  exposed  to  moisture,  they  may  be 


LOW   POTENTIAL   SYSTEMS.  143 

fished  on  the  loop  system,  if  separately  encased  throughout  in 
continuous  lengths  of  approved  flexible  tubing." 

An  illustration  of  wiring  on  the  "loop"  system  is  shown  in 
Figure  90.  This  system  makes  it  unnecessary  to  have  any 
concealed  joints  or  splices.  The  amount  of  wire  required  is 
somewhat  in  excess  of  that  required  for  tap  systems,  but  this 
is  often  balanced  by  a  saving  in  labor.  Sometimes,  however, 
the  labor  is  also  in  excess  of  that  required  for  tap  systems. 
The  main  advantage  of  the  system  is  that  all  joints  and  splices 
are  always  accessible.  The  figure  also  shows  mixed  "knob 
and  tube"  work  and  "conduit"  work.  Along  the  walls  behind 
the  furring  strips  there  is  seldom  sufficient  space  to  admit  of 
knob  and  tube  work  and  conduit  must  be  used. 

/.  "Mixed  concealed  knob  and  tube  work  as  provided  for 
in  No.  24  s,  must  comply  with  requirements  of  No.  24  n  to  p,  and 
No.  25,  when  conduit  is  used,  and  with  requirements  of  No. 
24  A,  when  armored  cable  is  used." 

«.  Must  at  all  outlets,  except  where  conduit  is  used,  be 
protected  by  approved  flexible  insulating  tubing,  extending  in 
continuous  lengths  from  the  last  porcelain  support  to  at  least 
one  inch  beyond  the  outlet.  In  the  case  of  combination  fix- 
tures the  tubes  must  extend  at  least  flush  with  outer  end  of 
gas  cap. 

Figure  91  is  drawn  to  illustrate  "fish  work."  Fish  work  is 
used  in  finished  buildings,  mostly,  and  is  often  very  tedious 
and  expensive.  Hours  are  sometimes  spent  before  wires  can 
be  brought  through  and  often  the  effort  is  an  entire  failure. 
In  combination  work,  as  shown  in  Figure  77,  there  is  usually 
little  trouble,  as  there  is  the  whole  span  between  joists  to  run 
wires  in.  An  effort  to  fish  at  right  angles  to  the  joists  (when 
there  are  strips  under  joists)  is  more  difficult,  but  often  suc- 
cessful if  the  distance  is  not  too  great. 

When  there  are  two  men  the  usual  method  of  fishing  is : 
One  man  takes  a  wire  sufficiently  long  to  reach  from  one  open- 
ing to  the  other,  and,  after  bending  a  small  hook  on  one  end 


144 


MODERN   ELECTRICAL   CONSTRUCTION. 


in  such  a  way  that  it  will  not  catch  easily  on  obstructions, 
pushes  this  end  into  one  opening  and,  by  twisting  and  working 
backward  and  forward,  gradually  forces  it  toward  the  other 
opening.  At  this  opening  his  helper  is  stationed  with  a  short 
wire,  also  provided  with  a  hook,  with  which  he  must  seek  to 
catch  the  other  wire  when  it  comes  near  his  opening.  When 
the  two  wires  come  in  contact,  the  larger  one  is  drawn  out  and 
the  conducting  wires  (encased  in  approved  flexible  tubing) 
are  fastened  to  it  and  drawn  through.  The  tubing  should 
always  be  put  on  the  wires  before  drawing  in.  If  it  is  put  on 


Figure  91 

later  there  is  much  temptation  to  leave  it  as  indicated  at  the 
right  of  the  figure  at  a.  This  trick  is  quite  common,  but  is 
very  easily  detected  by  inspectors ;  the  wire  at  either  end  can 
easily  be  pushed  in  without  pushing  out  at  the  other,  as  it 
would  if  the  tubing  were  continuous.  If  the  tubing  has  been 
taped  to  the  wires  this  will  be  impossible,  but  either  one  of  the 
tubings  can  still  be  moved  without  moving  the  other,  which 
would  be  impossible  in  a  job  properly  done.  The  tubing  must 
consist  of  one  piece,  and  there  must  be  only  one  wire  in  each 
tubing. 


LOW   POTENTIAL   SYSTEMS.  145 

If  one  man  is  alone  on  a  fish  job,  a  handful  of  small  wire 
is  pushed  into  one  opening  in  a  manner  which  will  allow  it 
to  spread  out  considerably.  When  the  fish  wire  froni  the 
other  opening  comes  in  contact  with  it,  it  will  indicate  it  by 
moving  this  wire,  which  can  be  seen  by  that  left  hanging  out. 
A  small  fish  wire  is  then  used  to  draw  out  the  long  one.  If  the 
two  openings  are  in  different  rooms  and  not  visible,  one  from 
the  other,  a  bell  and  battery  can  be  used,  as  shown  in  the 
drawing,  if  there  are  no  wire  lath. 

When  wires  are  to  be  entirely  concealed  it  is  nearly  always 
necessary  to  find  a  way  through  headers,  timbers,  etc. ;  this 
can  hardly  be  done  without  cutting  holes  in  plaster.  A  method 
doing  as  little  damage  as  any  is  shown  at  the  top  in  Figure  91. 
A  hole  is  bored  through  the  2X4,  which  will  allow  the  wire, 
when  job  is  finished,  to  continue  downward  as  shown  by  dotted 
lines,  1  and  2.  Such  turns  are  seldom  ever  used  with  electric 
light  wires  on  account  of  their  size;  they  are  more  practicable 
with  bell  or  telephone  wires. 

Where  it  is  desired  to  keep  wires  from  showing  in  a  parlor, 
for  instance,  they  can  be  fished  from  an  adjoining  room,  as 
indicated  by  dotted  line  3,  where  the  wires  are  run  down 
partition  in  moulding  in  closet  and  then  through  to  switch, 
which  is  in. the  same  room  with  the  lights.  Before  under- 
taking a  job  of  fish  work  it  is  well  to  look 'the  whole  building 
over  carefully.  There  are  often  false  walls  along  chimneys, 
especially  at  both  sides  of  mantels,  in  which  wires  can  be 
easily  run  from  basement  to  attic. 

Often  it  may  be  necessary  to  remove  baseboards  in  order 
to  find  room  for  wires.  When  removing  such  boards  never 
attempt  to  drive  nails  out,  always  break  them  off;  if  driven 
out  they  will  usually  split  off  parts  of  the  board. 

Soft  wood  floors  can  easily  be  taken  up  when  necessary. 
Use  a  broad  thin  chisel  and  cut  away  the  tongue  on  each  side 


14  ,  MODERN   ELECTRICAL  CONSTRUCTION. 

of  the  board  to  be  taken  up;  the  board  can  then  be  readily 
taken  up.  With  double  floors  or  with  tightly  laid  hardwood 
floors,  it  is  better  to  cut  pockets  in  ceiling  below. 

For  Fixture  Work. 

r.  Must  have  an  approved  rubber  insulating  covering  (see 
No.  46),  and  be  not  less  in  size  than  No.  18  B.  &  S.  gage. 

w.  Supply  conductors,  and  especially  the  splices  to  fixture 
wires,  must  be  kept  clear  of  the  grounded  part  of  gas  pipes, 
and,  where  shells  or  outlet  boxes  are  used,  thqy  must  be  made 
sufficiently  large  to  allow  the  fulfillment  of  this  requirement. 

x.  Must,  when  fixtures  are  wired  outside,  be  so  secured 
as  not  to  be  cut  or  abraided  by  the  pressure  of  the  fastenings 
or  motion  of  the  fixture. 

y.  Under  no  circumstances  must  there  be  a  difference  of 
potential  of  more  than  300  volts  between  wires  contained  in  or 
attached  to  the  same  fixture. 

Rule  24  A.     New  Rule.     Armored  Cables. 
(For  Construction  Rules  sec  No.  48.) 

a.  Must  be  continuous  from  outlet  to  outlet  or  to  junction 
boxes,  and  the  armor  of  the  cable  must  properly  enter  and  be 
secured  to  all  fittings. 

NOTE — In  case  of  underground  service  connections  and  main 
runs,  this  involves  running  such  armored  cable  continuously 
into  a  main  cut-out  cabinet  or  gutter  surrounding  the  panel 
board,  as  the  case  may  be.  (See  No.  54.) 

b.  Must  be  equipped  at  every  outlet  with  an  approved  out- 
let box  or  plate,  as  required  in  conduit  work.     (See  No.  49 
/  to  o.) 

Note. — Outlet  plates  must  not  be  used  where  it  is  practicable 
to  install  outlet  boxes. 

In  buildings  already  constructed  where  the  conditions  are 
such  that  neither  outlet  box  nor  plate  can  be  installed,  these 
appliances  may  be  omitted  by  special  permission  of  the  Inspec- 
tion Department  having  jurisdiction,  provided  the  armored 
cable  is  firmly  and  rigidly  secured  in  place. 

c.  Must  have  the  metal  armor  of  the  cable  permanently 
and  effectively  grounded. 


LOW   POTENTIAL   SYSTEMS.  147 

NOTE — It  Is  essential  that  the  metal  armor  of  such  systems 
be  joined  so  as  to  afford  electrical  conductivity  sufficient  to 
allow  the  largest  fuse  or  circuit  breaker  in  the  circuit  to  operate 
before  a  dangerous  rise  in  temperature  in  the  system  can  occur. 
Armor  of  cables  and  gas  pipes  must  be  securely  fastened  in 
metal  outlet  boxes  so  as  to  secure  good  electrical  connection. 
Where  boxes  used  for  centers  of  distribution  do  not  afford  good 
electrical  connection,  the  armor  of  the  cables  must  be  joined 
around  them  by  suitable  bond  wires.  Where  sections  of  ar- 
mored cable  are  installed  without  being  fastened  to  the  metal 
structure  of  buildings  or  grounded  metal  piping,  they  must 
be  bonded  together  and  joined  to  a  permanent  and  efficient 
ground  connection. 

d.  When  installed  in  so-called  fireproof  buildings  in  course 
of  construction  or  afterwards  if  concealed,  or  where  it  is  ex- 
posed to  the  weather,  or  in  damp  places  such  as  breweries, 
stables,  etc.,  the  cable  must  have  a  lead  covering  at  least  1/32 
of  an  inch  in  thickness  placed  between  the  outer  braid  of  the 
conductors  and  the  steel  armor. 

e.  Where  entering  junction  boxes  at  all  other  outlets,  etc., 
must  be  provided  with  approved  terminal  fittings  which  will 
protect  the  insulation  of  the  conductors  from  abrasion,  unless 
such  junction  or  outlet  boxes  are  specially  designed  and  ap- 
proved for  use  with  the  cable. 

f.  Junction  boxes  must  always  be  installed  in  such  a  man- 
ner as  to  be  accessible. 

g.  For  alternating  current  systems  must  have  the  two  or 
more  conductors  of  the  cable  enclosed  in  one  metal  armur. 

25.    Interior  Conduits. 

(Sec  also  Nos.  24  n  to  p,  and  49.) 

The  object  of  a  tube  or  conduit  is  to  facilitate  the  insertion 
or  extraction  of  the  conductors  and  to  protect  them  from  me- 
chanical injury.  Tubes  or  conduits  are  to  be  considered  merely 
as  raceways,  and  are  not  to  be  relied  upon  for  insulation  be- 
tween wire  and  wire,  or  between  the  wire  and  the  ground. 

The  installation  of  wires  in  conduit  not  only  affords  the 
wires  protection  from  mechanical  injury,  but  also  reduces  the 
liability  of  a  short  circuit  or  ground  on  the  wires  producing 
an  arc,  which  would  set  fire  to  the  surrounding  material;  the 
conduit  being  generally  of  sufficient  thickness  to  blow  a  fuse 
before  the  arc  can  burn  through  the  metal  of  the  pipe.  For 


148  MODERN   ELECTRICAL  CONSTRUCTION. 

this  reason  the  wires  should  be  entirely  encased  in  metal 
throughout,  both  in  the  conduit  and  at  all  outlets.  Another 
advantage  derived  from  the  use  of  iron  conduit  is  the  facility 
with  which  wires  can  be  extracted  and  replaced  in  case  a 
fault  develops  on  any  of  them.  The  saving  which  this  may 
mean  in  cases  where  the  installation  of  new  wires  would 
necessitate  the  destruction  of  costly  decorations  can  readily  be 
seen.  It  must  be  remembered  that  the  arc  or  burn  produced 
by  a  short  circuit  or  ground  is  proportional  to  the  size  of  the 
fuse  protecting  the  circuit.  If  a  large  fuse,  say  30  amperes,  is 
used  to  protect  a  branch  circuit  and  a  ground  or  short  occurs 
on  this  circuit,  the  wire  may  become  fused  to  the  pipe  so  that 
it  cannot  easily  be  pulled  out.  This  is  one  reason  why  fuses 
should  be  as  small  as  practicable.  More  than  six  amperes  is 
seldom  used  on  branch  circuits,  so  that  no  larger  fuse  than 
this  should  ordinarily  be  used.  The  installation  of  wires  in 
iron  conduit  also  reduces  the  liability  of  lightning  discharges 
entering  a  building  as  the  pipe  surrounding  the  wires  offers 
great  resistance  to  the  passage  of  these  sudden  currents. 

Conduit  is  classed  under  two  general  heads,  lined  and  tin- 
lined.  In  both  classes  of  conduit  the  same  thickness  of  metal 
is  required. 

a.  No  conduit  tube  having  an  internal  diameter  of  less 
than  five  eighths  of  an  inch  shall  be  used.  Measurements  to 
be  taken  inside  of  metal  conduits. 

This  rule  favors  lined  conduit  insomuch  that  it  requires 
the  same  pipe  for  lined  and  unlined,  and  allows  a  lined  con- 
duit of  less  than  five-eighths  of  an  inch  in  diameter. 

6.  Must  be  continuous  from  outlet  to  outlet  or  to  junc- 
tion boxes,  and  the  conduit  must  properly  enter,  and  be  secured 
to  all  fittings. 

In  case  of  underground  service  connections  and  main  runs, 
this  involves  running  each  conduit  continuously  into  a  main 
cut-out  cabinet  or  gutter  surrounding  the  panel  board,  as  the 
case  may  be  (see  No.  54.) 

When  conduit  is  used  every  run  of  pipe  must  end  in  acces- 


LOW   POTENTIAL   SYSTEMS. 


149 


sible  outlet  boxes.  This  box  may  be  a  cutout  center,  switch 
outlet,  fixture  outlet  or  a  junction  box.  If  a  mixed  form  of 
wiring  is  used,  where  part  of  a  circuit  is  run  in  conduit  and 
the  balance  with  some  other  form  of  construction,  such  as 
concealed  knob  and  tube  work,  for  instance,  the  conduit  must 
in  all  cases  enter  the  box  and  be  firmly  attached  to  it,  as 
shown  in  Figure  92..  Cases  are  sometimes  found  where  the 
conduit  is  brought  just  to  the  box,  but  does  not  enter  it,  the 


•—Junction  bo» 


Figure  92 

wires  being  extended  through  holes  into  the  box.  This  method 
of  wiring  is  obviously  wrong;  as  a  wireman  is  apt  to  find  if 
he  ever  has  occasion  to  replace  wires  in  such  a  system.  The 
same  holds  true  of  cutout  centers.  Here  also  every  run  of 
conduit  must  enter  the  box.  The  conduit  should  not  simply 
be  brought  to  the  sides  or  the  back  of  the  cutout  center  and 
the  wires  then  carried  to  the  cutouts  in  flexible  tubing,  but 
every  conduit  should  enter  clear  into  the  box  so  that  when 
the  work  is  completed  there  will  be  no  exposed  wiring.  In 


150 


MODERN   ELECTRICAL   CONSTRUCTION. 


the  case  of  main  runs  the  conduit  should  enter  the  boxes  and 
never  be  broken  between  the  outlets.  Sometimes  it  is  neces- 
sary to  install  meters  on  the  mains  and  the  conduit  is  ended 
and  the  wires  carried  to  the  meters  and  then  either  extended 
in  conduit  or  carried  into  the  cutout  center.  This  construc- 
tion should  be  avoided.  If  a  meter  is  to  be  installed  near  a 
cutout  center,  the  main  conduit  should  be  carried  into  the  box 
and  the  necessary  meter  loops  then  brought  out.  In  this  way 


Figure  93 

the  quantity  of  wire  outside  of  conduits  is  reduced  to  a  mini- 
mum. If  a  meter  is  to  be  installed  in  some  location  along  the 
mains  other  than  at  the  cutout  center  or  service  switch,  a 
junction  box  should  be  provided  and  the  meter  loops  brought 
out  from  that.  This  is  shown  in  Figure  93,  which  also  shows 
a  cutout  box  as  used  with  conduit  systems. 

c.    Must  be  first  installed  as  a  complete  conduit  system, 
without  the  conductors. 

As  fast  as  the  conduit  is  installed,  the  ends  of  the  pipes 


LOW   POTENTIAL   SYSTEMS.  151 

should  be  closed,  using  paper  or  corks.  This  does  away  with 
the  liability  of  plaster  or  other  substances  entering  the  pipes 
and  causing  trouble  when  the  \vires  are  to  be  pulled  in.  The 
conductors  shoilld  not  be  pulled  in  until  all  the  mechanical  work 
on  the  building  is,  as  far  as  possible,  finished.  When  a  con- 
duit system  is  ready  for  the  wires,  the  "pulling  in"  may  be 
done  in  various  ways.  For  short  runs,  all  that  is  necessary  is 
to  shove  the  wires  in  at  one  opening  until  they  come  out  at 
the  other.  If  a  run  is  too  long  to  be  inserted  in  this  way, 
what  is  known  cs  a  "fish  wire"  can  be  used.  The  ordinary 
fish  wire  is  a  flat  band  of  steel  about  5/32  inch  wide  and  1/32 
inch  thick.  This  wire  can  be  forced  through  any  ordinary 
length  of  pipe.  Ordinary  round  steel  wire  of  about  No.  12 
or  14  B.  &  S.  gauge  can  also  be  used  for  fish  wire,  although  this 
is  not  as  good  as  the  fish  wire  above  described. 

The  end  of  the  wire  is  first  bent  back  so  as  to  form  a  very 
small  hook  or  eye;  this  will  enable  it  to  slide  easily  over  ob- 
structions in  the  pipe  and  also  make  it  possible  should  it  stick 
somewhere  to  engage  it  with  another  fish  wire  provided  with 
a  suitable  hook  and  entered  from  the  other  end  of  the  pipe. 
This  is  very  often  necessary  in  runs  having  many  bends.  The 
fish  wire,  having  been  pushed  through  the  pipe,  is  now  fastened 
to  the  copper  wire  by  means  of  a  strong  hook  and  the  copper 
wire  pulled  into  the  pipe. 

In  pulling  in  the  large  size  cables,  it  is  often  found  advan- 
tageous to  pull  on  the  fish  wire  and  at  the  same  time  push  on 
the  end  of  the  cable  entering  the  pipes.  It  is  also  well  to 
remember  that  it  is  easier  to  pull  down  than  to  pull  up,  as, 
when  pulling  down,  the  weight  of  the  cable  assists.  The  use 
of  soapstone  facilitates  the  drawing  in  of  the  wires.  The  wire 
may  either  be  covered  with  the  powdered  soapstone  or  the 
soapstone  may  be  blown  into  the  pipes.  An  elbow  partly 
filled  with  soapstone  is  often  found  convenient  for  blowing  the 
soapstone  into  the  pipe,  always  blowing  from  the  highest  point. 


152  MODERN   ELECTRICAL  CONSTRUCTION. 

d.  Must  be  equipped  at  every  outlet  with  an  approved  out- 
let box  or  plate  (see  No.  49  /to  0). 

Outlet  plates  must  not  be  used  where  it  is  practicable  to 
install  outlet  boxes. 

In  buildings  already  constructed  where  the  conditions  are 
such  that  neither  outlet  box  nor  plate  can  be  Installed,  these 
appliances  may  be  omitted  by  special  permission  of  the  Inspec- 
tion Department  having  jurisdiction,  providing  the  conduit  ends 
are  bushed  and  secured. 

The  object  of  an  outlet  box  is  to  hold  the  conduits  firmly 
in  place,  to  connect  the  various  runs  of  conduit  so  that  they 
form  a  continuous  electrical  path  to  the  ground,  and  to  afford 
a  fireproof  enclosure  for  the  joints,  switches,  etc.  Outlet 
boxes  are  made  in  various  designs  to  meet  the  requirements 
of  the  work  on  which  they  are  to  be  used. 

Where  it  is  impossible  to  use  an  outlet  box,  an  outlet  plate 
can  be  used.  These  plates  are  fitted  with  set  screws  so  that 
they  hold  the  ends  of  the  conduits  firmly  in  position  and  make 
the  metal  of  the  system  continuous.  They  do  not  afford  a 
fireproof  enclosure  for  the  joints  and  for  that  reason  should 
never  be  used  when  it  is  practicable  to  use  an  outlet  box.  If 
the  conditions  are  such  that  neither  an  outlet  box  or  plate  can 
be  used,  special  permission  can  be  obtained  from  the  Inspec- 
tion Department  having  jurisdiction  to  omit  them.  In  this 
case  the  conduits  should  be  bushed  at  the  ends  and  the  pipes 
should  be  bonded  together. 

c.  Metal  conduits  where  they  enter  junction  boxes,  and  at 
all  other  outlets,  etc.,  must  be  provided  with  approved  bushings 
fitted  so  as  to  protect  wire  from  abrasion,  except  when  such 
protection  is  obtained  by  the  use  of  approved  nipples,  properly 
fitted  in  boxes  or  devices. 

When  a  piece  of  conduit  is  cut  with  a  pipe  cutter,  a  sharp 
edge  is  left  on  the  inside.  This  edge,  if  left  on,  would  soon 
cut  into  the  insulation  of  the  wires.  It  should  be  removed  by 
means  of  a  pipe  reamer.  The  bushing  can  now  be  screwed  on 
as  shown  in  Figure  92,  a  locknut  having  first  been  screwed 


LOW   POTENTIAL   SYSTEMS.  153 

onto  the  pipe.     The  locknut  and  bushing  are  then  screwed  up 
so  that  they  are  tight  and  .form  a  good  connection. 

/.  Must  have  the  metal  of  the  conduit  permanently  and 
effectually  grounded. 

It  is  essential  that  the  metal  of  conduit  systems  be  joined 
so  as  to  afford  electrical  conductivity  sufficient  to  allow  the 
largest  fuse  or  circuit  breaker  in  the  circuit  to  operate  before 
a  dangerous  rise  in  temperature  in  the  conduit  system  can 
occur.  Conduits  and  gas  pipes  must  be  securely  fastened  in 
metal  outlet  boxes  so  as  to  secure  good  electrical  connection. 
Where  boxes  used  for  centers  of  distribution  do  not  afford 
good  electrical  connections,  the  conduits  must  be  joined 
around  them  by  suitable  bond  wires.  Where  sections  of  metal 
conduit  are  installed  without  being  fastened  to  the  metal  struc- 
ture of  buildings  or  grounded  metal  piping,  they  must  be  bonded 
together  and  joined  to  a  permanent  and  efficient  ground  con- 
nection. 

That  the  metal  in  a  conduit  system  should  be  permanently 
and  effectually  grounded  is  plainly  evident  when  the  hazards 
which  are  present  with  ungrounded  or  poorly  grounded  con- 
duit are  recalled.  Until  recently  very  little  attention  has 
been  given  to  the  matter  of  properly  grounding  conduits,  but 
with  the  increased  use  the  necessity  of  so  doing  has  become 
very  apparent.  If  the  bare  wire  of  one  side  of  a  system  conies 
in  contact  electrically  with  the  iron  pipe,  and  if  there  is  a 
ground  on  the  other  side  of  the  system  (and  there  always  is 
with  3-wire  systems)  the  conduit  becomes  a  conductor.  If 
the  conduit  system  is  so  installed  that  every  piece  is  in  good 
electrical  connection  and  the  entire  system  effectually  grounded 
no  harm  will  be  done  except  the  blowing  of  a  fuse.  Conduit  is 
installed  in  all  kinds  of  locations.  It  may  be  in  contact  with  a 
gas  pipe,  lead  pipe,  or  run  in  a  damp  floor,  or  it  may  be  run 
exposed  where  a  person  could  easily  come  in  contact  with  it. 
The  effects  that  might  result  from  a  conduit  so  run  should  the 
conduit  become  alive  are  readily  seen.  Suppose  that  in  the 
first  case  the  conduit  crosses  the  gas  pipe  at  right  angles,  the 
area  of  contact  would  be  very  small  and  the  effect  of  the  cur- 
rent in  a  livened  conduit  crossing  this  poor  contact  would 


154  MODERN   ELECTRICAL  CONSTRUCTION. 

result  in  burning  a  hole  in  the  gas  pipe  and  igniting  the  escap- 
ing gas.  Again,  suppose  the  conduit  run  in  a  damp  floor 
should  become  alive ;  the  damp,  wood  work,  being  a  conductor, 
would  soon  char  and  the  charred  part  would  then  readily 
ignite.  With  a  system  which  is  grounded,  an  exposed  piece 
of  conduit  will  usually  only  be  alive  for  a  very  short  time 
during  the  blowing  of  the  fuse.  Even  if  it  remains  perma- 
nently alive,  current  will  not  flow  from  it  to  the  surrounding 
material,  but  will  take  the  easiest  path  to  ground;  which  is 
along  the  conduit.  On  the  ordinary  branch  circuits,  the  vari- 
ous runs  of  conduit  are  bonded  together  through  the  outlet 
boxes  and,  in  connecting  the  conduits  to  these  boxes,  care  must 
be  taken  that  they  make  good  contact.  In  order  to  do  this,  the 
conduit  should  enter  at  right  angles  to  the  box  and  the  enamel 
should  be  scraped  away  from  the  box  so  that  the  locknut  and 
bushing  make  good  electrical  connection.  The  same  thing 
should  be  done  where  the  conduit  enters  the  cutout  box.  The 
metal  of  the  cutout  box  will  bond  together  the  various  branch 
conduits  and  the  main  conduit.  The  main  conduit  should  now 
be  connected  to  some  good  ground,  such  as  a  water  or  steam 
pipe  or  metal  work  of  the  building.  Never  carry  the  ground 
wire  to  a  gas  pipe.  The  various  branch  conduits  should  also 
be  grounded  wherever  possible,  at  and  on  metal  beams  over 
which  they  cross  and  at  every  gas  outlet.  The  reason  of 
grounding  the  gas  pipe  thoroughly  at  the  gas  outlets  is  to  be 
sure  of  a  good  ground.  The  gas  pipe  is  necessarily  in  contact 
with  the  outlet  box  at  this  point  and  any  poor  contact  which 
might  cause  arcing  must  be  avoided. 

Strictly  speaking,  a  conduit  should  be  grounded  with  a  wire 
equal  to  that  usea  in  the  conduit.  This  can  easily  be  done  in 
the  case  of  smaller  circuits,  but  with  the  larger  size  mains  it  is 
a  more  difficult  matter.  No  special  device  has  as  yet  been 
designed  for  the  ground  wire  connection,  the  usual  practice 
being  to  take  a  number  of  good  turns  around  the  conduit  and 


LOW   POTENTIAL   SYSTEMS.  155 

then  solder  the  wire  to  the  conduit  and  tape  the  joint.  A 
better  way  would  be  to  use  a  few  T  couplings  on  the  system 
and  to  screw  brass  plugs  to  these  and  solder  the  ground  wire 
to  the  plugs.  Such  couplings  should  be  installed  near  outlets 
where  they  will  not  interfere  much  with  "fishing." 

If  the  ground  wire  has  to  be  run  for  any  great  distance, 
it  should  be  installed  as  though  it  were  at  all  times  alive,  and 
should  be  kept  away  from  inflammable  material.  The  method 
advised  under  13  A  for  grounding  wires  should  be  used. 
Where  a  3-wire  system  is  used,  the  best  ground  obtainable  is 
the  neutral  wire  of  the  system.  When  a  ground  is  made  to 
the  neutral  wire,  it  should  be  made  back  of  the  fuses  on  the 
service  switch ;  never  make  the  connection  with  the  neutral 
inside  of  the  service  switch. 

g.  Junction  boxes  must  always  be  installed  in  such  a 
manner  as  to  be  accessible. 

h.  All  elbows  or  bends  must  be  so  made  that  the  con- 
duit or  lining  of  same  will  not  be  injured.  The  radius  of  the 
curve  of  the  inner  edge  of  any  elbow  not  to  be  less  than  three 
and  one-half  inches.  Must  have  not  more  than  the  equivalent 
of  four  quarter  bends  from  outlet  to  outlet,  the  bends  at  the 
outlets  not  being  counted. 

If  more  than  four  quarter  bends  are  necessary,  a  junction 
box  should  be  installed  and  the  wires  first  pulled  from  one 
of  the  outlets  to  the  junction  box  and  then  from  the  junction 
box  to  the  other  outlet. 

Several  methods  are  in  use  for  bending  conduit.  With  the 
lined  conduit  elbows  and  bends  of  various  shapes  can  be 
obtained  already  bent,  and  it  is  much  more  satisfactory  to  use 
these,  as  considerable  care  must  be  exercised  in  making  bends 
in  order  to  keep  the  inside  lining  from  coming  loose  from 
the  pipe  and  causing  trouble  when  ''pulling  in."  To  prevent 
this  a  suitable  spiral  spring  is  sometimes  inserted  into  the  con- 
duit before  bending.  Plumbers  working  with  lead  pipe  often 
use  coarse  sand  to  fill  the  pipe  before  bending.  This  is  more 


156 


MODERN   ELECTRICAL   CONSTRUCTION. 


particularly  useful  with  special  conduits  such  as  brass  tubing, 
which  is  sometimes  used  in  showcase  or  window  work  and 
classed  with  fixtures. 

With  unlined  conduits  the  bending  is  a  simple  matter, 
although  here  also  care  must  be  taken  to  see  that  the  conduit 
does  not  bend  flat.  In  a  good  bend  the  pipe  retains  its  circular 
form  throughout  the  bend,  while,  if  the  bend  is  poorly  made, 
the  pipe  will  assume  an  oval  shape,  flattening  somewhat  at 
the  bend.  The  smaller  size  conduits  can  be  bent  in  a  common 
vise.  This  is  best  accomplished  by  gripping  the  pipe  in  the 


Figure  94 


vise  and  making  a  small  bend,  then  moving  the  pipe  for  a  slight 
distance  and  bending  again,  and  continuing  until  the  desired 
shape  is  obtained.  Another  method  which  can  be  used  on 
small  pipes  is  shown  at  a  in  Figure  94,  using  a  three  or  four 
foot  length  of  gas  pipe  or  conduit  with  an  ordinary  gas  pipe  T 
on  the  end.  This  is  run  over  the  conduit  and  gives  sufficient 
leverage  to  make  any  bend. 

A  simple  device  used  for  bending  conduits  is  shown  at 
b  in  Figure  94.  This  is  constructed  of  metal,  the  wheel  being 
grooved  to  fit  the  pipe.  A  similar  device,  minus  the  wheel 
and  lever,  may  be  made  up  of  two  blocks  of  wood  firmly 
fastened  to  a  work  bench.  The  pipe  can  be  bent  around  this 
by  hand. 

For  the  larger  size  conduits,  elbows  can  be  obtained  already 
bent.  Connections  between  the  various  lengths  of  conduit  are 


LOW  POTENTIAL  SYSTEMS.  157 

made  with  the  ordinary  gas-pipe  couplings.  When  the  conduit 
comes  from  the  factory  each  Jength  of  pipe  is  provided  with  a 
coupling  at  one  end.  (This  practice  is  now  being  discon- 
tinued, the  couplings  being  left  off.)  This  coupling  should  be 
removed  and  the  end  of  the  conduit  reamed  out.  The  reaming 
should  always  be  done  so  that  there  is  considerable  metal  left 
at  the  end  of  the  pipe,  and  it  should  never  be  carried  so  far  as 
to  leave  only  a  sharp  edge.  If  a  thread  is  to  be  cut,  it  is  good 
practice  to  take  a  couple  of  turns  with  the  reamer  after  this  has 
been  done.  The  coupling  can  then  be  screwed  on.  When 
making  the  connection,  the  pipes  should  be  screwed  into  the 
coupling  so  that  the  ends  just  "butt."  Do  not  attempt  to  screw 
them  too  tight,  or,  in  all  probability,  the  thread  on  the  end 


Figure  95 

of  the  pipe  will  be  turned  in  and  close  the  opening.  Figure 
95,  a,  shows  how  a  connection  should  be  made.  If  lined  con- 
duit is  not  properly  reamed  and  is  screwed  too  tight,  the 
opening  is  often  entirely  closed  or  forced  inward,  as  shown 
at  b. 

It  is  often  necessary,  especially  in  making  changes  in  old 
installations,  to  fit  pieces  between  two  pipes,  neither  one  of 
which  can  be  turned  so  as  to  draw  them  together.  In  such 
cases  a  long  thread  is  cut  on  one  piece  of  the  pipe  and  the 
coupling  run  back  on  it ;  when  the  pipes  are  butted  together 
the  coupling  is  run  over  the  two  pipes,  thus  connecting  them. 
A  locknut  may  be  run  upon  either  pipe  and  used  to  keep  the 
coupling  in  place. 

In  running  conduits  avoid  as  much  as  possible  passing 
through  bath-rooms  and  other  places  where  plumbers  are 
likely  to  run  their  piping. 


158  MODERN   ELECTRICAL   CONSTRUCTION. 

When  practicable,  conduits  should  be  run  so  they  will  drain ; 
for  instance,  where  crossing  a  room  from  one  side  bracket  to 
another,  it  is  better  to  run  along  ceiling  than  along  the  floor. 
Conduits  will  sometimes  become  quite  moist  inside  from  con- 
densation. Where  there  is  any  likelihood  of  this  the  ends  may 
be  sealed. 

26.    Fixtures. 

(Sec  also  Nos.  22  e,  24  v  to  x.) 

a.  Must  when  supported  from  the  gas  piping  or  any 
grounded  metal  work  of  a  building  be  insulated  from  such 
piping  or  metal  work  by  means  of  approved  insulating  joints 
(see  No.  59)  placed  as  close  as  possible  to  the  ceiling. 

"Gas  outlet  pipes  must  be  protected  above  the  insulating 
joint  by  approved  insulating  tubing,  and  where  outlet  tubes 
are  used  they  must  be  of  sufficient  length  to  extend  below 
the  insulating  joint,  and  must  be  so  secured  that  they  will  not 
be  pushed  back  when  the  canopy  is  put  in  place 

"Where  canopies  are  placed  against  plaster  walls  or  ceilings 
in  fireproof  buildings,  or  against  metal  walls  or  ceilings,  or 
plaster  walls  or  ceilings  on  metallic  lathing  in  any  class  of 
buildings,  they  must  be  thoroughly  and  permanently  insulated 
from  such  walls  or  ceilings." 

Figure  96  shows  insulating  joints  such  as  are  used  to  insu- 
late fixtures  from  the  gas  piping  of  buildings. 

The  object  of  an  insulating  joint  is  to  prevent  a  "ground" 


Figure  96 

on  one  fixture  from  causing  trouble  on  other  fixtures.  If,  for 
instance,  one  fixture  in  a  building  were  in  contact  with  the 
positive  wire  of  the  system  and  another  in  contact  with  a  nega- 
tive wire,  and  the  two  fixtures  connected  direct  to  the  gas 


LOW    POTENTIAL   SYSTEMS. 


159 


piping,  the  two  contacts  or  "grounds"  would  form  a  short  cir- 
cuit; the  current  flowing  from  one  pole  along  the  gas  piping  to 
the  other.  This  becomes  impossible  when  the  fixtures  are 
insulated  from  the  piping,  or  conducting  parts  of  ceilings. 

Insulating  joints  are  made  in  a  variety  of  patterns.  The 
one  shown  at  a  in  Figure  96  is  designed  for  use  on  a  combina- 
tion gas  and  electric  fixture,  and  is  made  to  allow  the  gas  to 
pass  through.  Other  forms,  such  as  b,  can  be  used  on  conduit 
work  to  connect  to  the  stub  in  the  outlet  box,  or  on  a  gas  outlet 
where  it  is  desired  to  use  the  electric  light  only. 

Insulating  joints  should  be  placed  as  close  as  possible  to  the 
ceiling,  so  that  there  will  be  a  minimum  of  exposed  pipe  above 


Figure  97 

the  joint.  If  the  gas  pipe  has  been  left  long  so  that  the  insu- 
lating joint  comes  some  distance  below  the  ceiling,  it  is  a  good 
plan  to  protect  the  pipe  above  the  joint  either  by  using  a  porce- 
lain tube  which  will  fit  over  the  pipe  or  by  taping  the  pipe 
thoroughly.  Flexible  tubing  is  also  sometimes  used.  See 
Figure  97. 

In  connecting  the  fixture,  care  should  be  taken  that  the 
extra  wire  usually  left  for  making  the  joint  is  twisted  around 
the  pipe  below  the  insulating  joint;  never  above.  If  the  wires 
at  the  outlet  have  been  properly  run,  as  shown  in  Figure  97, 
the  flexible  tubing  will  extend  to  the  bottom  of  the  insulating 
joint. 


160 


MODERN   ELECTRICAL   CONSTRUCTION. 


When  a  straight  electric  fixture  is  to  be  installed  on  some 
grounded  part  of  the  building,  a  crowfoot,  shown  at  c,  Figure 
96,  can  be  fastened  to  the  metal  work  and  the  fixture  then  con- 
nected with  the  insulating  joint. 

If  the  fixture  is  to  be  mounted  on  plaster,  a  hardwood 
block  can  be  screwed  to  the  wall  or  ceiling  and  a  crowfoot 
screwed  to  this.  The  screws  holding  the  crowfoot  must  not 
extend  through  the  block.  Such  a  case  is  illustrated  at  the 
right  in  Figure  97. 

Before  the  plastering  is  put  on,  a  board  should  be  fastened 
between  the  joists,  so  that  the  wooden  block  may  later  be 
screwed  to  it.  This  is  not  absolutely  necessary,  as  screws  in 
lath  will  usually  hold  light  fixtures.  Heavy  fixtures  in  old 


Figure  98 


buildings  can  best  be  hung  as  shown  at  b,  in  Figure  98.  This 
method  is  also  used  for  ceiling  fan  motors.  These  motors 
must  never  be  rigidly  fastened,  but  should  always  be  left  free 
to  swing  and  find  their  own  centers. 

In  connection  with  open  or  moulding  work,  the  canopies 
should  always  be  cut  out,  so  that  the  loom  or  moulding  may 
enter  them.  On  no  account  should  wires  be  allowed  to  rest 
on  sharp  edge  of  canopy.  See  a,  Figure  98. 

Figure  98  illustrates  at  c  how  fixtures  are  fastened  to  tile 
ceilings,  toggle  bolts  and  a  metal  strip  to  which  a  piece  of  pipe 
is  fastened  being  used. 


LOW   POTENTIAL   SYSTEMS.  161 

Fiber  is  often  used  for  the  insulation  of  canopies  from  the 
ceiling.  Figure  98  at  d  shows  a  bug  insulator,  which  can  be 
used  for  this  purpose.  A  hole  is  drilled  in  the  center  of  a 
small  block  of  fiber,  and  it  is  then  slotted  lengthwise  with  a 
saw.  A  small  dent  is  made  in  the  upper  edge  of  the  canopy 
and  the  fiber  blcck  slipped  on  the  edge,  so  that  the  small  dent 
fits  into  the  hole.  If  a  hole  is  punched  through  the  edge  of 
the  canopy,  and  a  brass  pin  riveted  in,  a  much  better  job  is 
obtained.  Short,  thin  strips  of  fiber,  or  a  long  strip  riveted  to 
the  inside  of  the  canopy  and  left  to  project  about  one-eighth 
inch,  are  often  used.  These  being  placed  on  the  inside  of  the 
canopy  are  much  more  sightly  than  the  bug  insulators.  When 
a  wooden  block  is  used  to  fasten  the  fixture  to  the  wall,  the 
block  may  be  made  large  enough  so  that  the  canopy  will  fit 
against  it.  The  practice  of  fastening  the  canopy  a  short  dis- 
tance from  the  ceiling  does  not  comply  with  the  rule. 

b.  Must  have  all  burs,  or  fins,  removed  before  the  con- 
ductors are  drawn  into  the  fixture. 

c.  Must  be  tested  for  "contacts,"  between  conductors  and 
fixture,  for  "short  circuits"  and  for  ground  connections  before 
it  is  connected  to  its  supply  conductors. 

Fixtures  are  always  made  up  of  gas  piping  and  their  con- 
struction is,  therefore,  very  similar  to  conduit  work. 

Three  tests  should  be  made  on  each  fixture  before  it  is  con- 
nected. If  tests  are  not  made  until  fixtures  have  been  con- 
nected, it  is  often  necessary  to  disconnect  them  again  to  de- 
termine whether  a  fault  is  in  the  fixture  or  in  the  wiring. 
Where  there  are  several  fixtures  on  one  circuit  arid  a  short 
circuit  should  be  discovered,  it  would  also  likely  be  necessary 
to  disconnect  several  of  them  before  the  right  one  would  be 
found. 

A  test  for  short  circuit  may  be  made,  first,  by  connecting 
the  two  wires  of  a  magneto  to  the  two  main  wires  at  top  of 
fixtures.  If  all  sockets  are  properly  connected  and  the  wiring 


162  MODERN   ELECTRICAL  CONSTRUCTION. 

is  clear,  no  ring  will  be  obtained.  If  a  ring  is  obtained,  it 
indicates  a  short  circuit. 

Without  changing  connections  each  socket  may  now  be 
tested  for  connections.  While  one  man  is  operating  the  mag- 
neto, another  may  insert  a  screw-driver,  jack-knife,  or  piece  of 
wire  into  each  socket  in  turn,  thus  connecting  the  two  termi- 
nals and  causing  a  ring  of  the  magneto.  Failure  to  obtain  a 
ring  would  indicate  an  open  circuit,  which  must,  of  course,  be 
remedied. 

The  third  test  is  made  for  "grounds."  To  make  it,  the  two 
fixture  wires  are  connected  to  one  wire  of  the  magneto  and 
the  other  wire  is  connected  to  the  metal  of  the  fixture. 

It  is  best  to  connect  this  wire  to  the  iron  piping,  and  not  to 
the  lacquered  brass ;  the  lacquer  is  often  a  very  good  insulator. 
If  a  ring  is  now  obtained,  it  indicates  that  the  insulation  on  a 
wire  has  been  damaged,  and  that  the  bare  wire  is  in  contact 
with  the  fixture.  This  test  can  be  made  more  thorough  by 
working  the  accessible  fixture  wires  back  and  forth  during  the 
test ;  sometimes,  a  damaged  portion  of  wire  is  not  in  contact 
with  the  metal  of  fixture  while  lying  upon  the  floor,  but  may  be 
brought  in  contact  with  it  when  hanging. 

Fixtures  that  have  been  connected  to  the  circuit  and  pro- 
vided with  insulating  joints  can  be  individually  tested  for 
"grounds,"  by  connecting  one  wire  of  a  magneto  to  the  body 
of  the  fixture  and  the  other,  first  to  one,  and  then  the  other, 
of  the  circuit  wires  in  the  sockets.  This  test  will  detect  a 
"ground"  in  a  fixture  without  disconnecting  it  from  the  cir- 
cuit. 

In  connecting  sockets  to  fixtures,  it  is  advisable  to  connect 
them  so  that  all  protruding  parts,  as  keys  or  receptacles  for 
lamps,  be  of  the  same  polarity,  that  is,  all  connected  to  the 
same  main  wire.  This  also  applies  to  reflectors,  border  lights 
for  theaters,  encased  in  metal,  etc.  This  will  not  lessen  the 
liability  of  such  parts  to  "ground,"  but  lessens  the  chances 


LOW   POTENTIAL  SYSTEMS.  163 

of  short  circuits  very  much.  Many  "shorts"  are  brought  about 
by  the  projecting  brass  lamp  butts  on  fixtures  being  of  opposite 
polarity.  If  they  are  of  the  same  polarity,  they  will  cause  no 
trouble. 

Special  fixtures  for  show  windows,  etc.,  are  often  made  up 
as  shown  in  Figure  99.  The  construction  shown  at  the  left  is 
more  compact  and  neat,  but  requires  more  care  in  installing 


Figure  99 


than  the  other,  because  of  the  edges  of  pipe  in  contact  with 
the  wires.  If  very  long  fixtures  of  this  kind  are  installed,  it  is 
advisable  to  insert  insulating  joints  as  often  as  practicable, 
even  if  necessary  to  run  wires  around  them. 

27.     Sockets. 

(For  construction  rules,  sec  No.  55.) 

a.  In  rooms  where  inflammable  gases  may  exist  the  incan- 
descent lamp  and  socket  must  be  enclosed  in  a  vapor-tight 
globe,  and  supported  on  a  pipe-hanger,  wired  with  approved 
rubber-covered  wire  (see  No.  41)  soldered  directly  to  the 
circuit. 

In  Figure  100,  a  shows  a  "vapor-tight"  globe  suspended  on 
a  pipe  hanger,  the  construction  of  which  complies  with  the 
requirements  of  this  rule.  If  moisture  is  present  it  is  well  to 
seal  the  upper  end  of  the  pipe  with  compound. 


164 


MODERN   ELECTRICAL  CONSTRUCTION. 


b.  In  damp  or  wet  places,  or  over  specially  inflammable 
stuff,  waterproof  sockets  must  be  used. 

Waterproof  sockets  should  be  hung  by  separate,  stranded, 
rubber-covered  wires,  not  smaller  than  No.  14  B.  &  S.  gage, 
which  should  preferably  be  twisted  together  when  the  pendant 
Is  over  three  feet  long.  These  wires  should  be  soldered  direct 
to  the  circuit  wires,  but  supported  independently  of  them. 

Waterproof  sockets  are  constructed  entirely  of  porcelain 
and  are  not  provided  with  keys,  therefore  the  circuits  to  which 
they  are  connected  must  be  controlled  by  switches.  As  a  gen- 
eral rule  these  sockets  are  furnished  with  a  short  piece  of 


Figure  100 

stranded,  rubber-covered  wire  extending  through  sealed  holes 
in  the  top  of  the  socket  and  the  supporting  wires  are  soldered 
to  them.  The  method  of  suspending  waterproof  sockets  varies 
with  the  conditions.  Ordinarily,  stranded  rubber-covered 
wires  of  the  proper  length  are  suspended  from  single  cleats  as 
shown  at  b,  in  Figure  100,  or,  if  the  line  knobs  are  large 
enough,  the  stranded  wire  may  be  supported  from  them.  If 
the  lamp  is  to  be  suspended  only  a  short  distance  from  the 


LOW   POTENTIAL   SYSTEMS.  165 

ceiling,  where  it  will  not  be  liable  to  be  disturbed,  it  may  be 
hung  from  two  ordinary  inch  porcelain  knobs,  as  shown  in 
Figure  81.  If  cleats  are  used  in  a  damp  place  for  supporting 
the  drop  a  half  cleat  must  be  provided  back  of  the  supporting 
cleat  to  give  a  one-inch  separation,  as  required  for  wires  in 
wet  places. 

28.    Flexible  Cord. 

a.  Must  have  an  approved  insulation  and  covering   (see 
No.  45). 

b.  Must   not   be   used    where   the   difference   of  potential 
between  the  two  wires  is  ove,r  300  volts. 

c.  Must  not  be  used  as  a  support  for  clusters. 

d.  Must  not  be  used  except  for  pendants,  portable  lamps 
or  motors,  and  portable  heating  apparatus. 

The  practice  of  making  the  pendants  unnecessarily  long  and 
then  looping  them  up  with  cord  adjusters  is  strongly  advised 
against.  It  offers  a  temptation  to  carry  about  lamps  which  are 
intended  to  hang  freely  in  the  air,  and  the  cord  adjusters  wear 
oft  the  insulation  very  rapidly. 

For  all  portable  work,  including  those  pendants  which  are 
liable  to  be  moved  about  sufficiently  to  come  in  contact  with 
surrounding  objects,  flexible  wires  and  cables  especially  de- 
signed to  withstand  this  severe  service  are  on  the  market,  and 
should  be  used.  (See  No.  45  f.) 

The  standard  socket  is  threaded  for  one-eighth-inch  pipe, 
and  if  it  is  properly  bushed,  the  reinforced  flexible  cord  will 
not  go  into  it,  but  this  style  of  cord  may  be  used  with  sockets 
threaded  for  three-eghths-inch  pipe,  and  provided  with  sub- 
stantial insulating  bushings.  The  cable  to  be  supported  inde- 
pendently of  the  overhead  circuit  by  a  single  cleat,  and  the  two 
conductors  then  separated  and  soldered  to  the  overhead  wires. 

The  bulb  of  an  incandescent  lamp  frequently  becomes  hot 
enough  to  ignite  paper,  cotton  and  similar  readily  ignitible 
materials,  and  in  order  to  prevent  it  from  coming  in  contact 
with  such  materials,  as  well  as  to  protect  it  from  breakage, 
every  portable  lamp  should  be  surrounded  with  a  substantial 
wire  guard. 

Flexible  cord  should  be  used  only  for  drop  lights  which 
hang  free  in  the  air,  or  for  desk  lights  or  fan  motors,  where 
the  cord  is  so  installed  that  it  is  not  liable  to  injury. 

Cord  adjusters  should  never  be  used  where  their  use  can 


166  MODERN   ELECTRICAL  CONSTRUCTION. 

be  avoided  and  where  they  are  installed  should  only  be  placed 
on  lamps  which  will  seldom  need  adjusting.  The  indis- 
criminate use  of  cord  adjusters  cannot  be  too  strongly  con- 
demned as  the  constant  rubbing  soon  destroys  the  insulation. 
At  c,  Figure  100,  shows  a  brass  socket  threaded  for  5^-inch 
pipe,  and  which  is  designed  to  be  used  with  portable  cord. 
Care  should  be  taken  in  making  up  these  sockets  to  see  that 
the  knot  under  the  head  of  the  socket  has  a  good  bearing 
surface  so  that  it  will  not  pull  through  the  larger  bushing,  these 
portables  being  very  apt  to  be  jerked  about. 

A  lamp  guard  to  be  of  any  value  should  be  so  constructed 
that  the  bulb  of  the  lamp  cannot  come  in  contact  with  any- 
thing outside  of  the  lamp  guard;  it  should  also  protect  the 
lamp  from  any  sudden  jar.  The  design  of  the  guard  should 
be  such  that  it  can  be  firmly  attached  to  the  socket  so  it  will 
not  work  loose  and  come  in  contact  with  the  live  butt  of  the 
lamp  or  projecting  threaded  portion  of  the  socket. 

c.     Must  not  be  used  in  show  windows. 

The  great  number  of  fires  which  have  been  caused  by  the 
use  of  flexible  cord  in  show  windows  is  sufficient  argument 
against  its  use.  Portable  cord,  or  what  is  kown  as  "show 
window"  cord,  should  be  used. 

/.  Must  be  protected  by  insulating  bushings  where  the 
cord  enters  the  socket. 

g.  Must  be  so  suspended  that  the  entire  weight  of  the 
socket  and  lamp  will  be  borne  by  knots  under  the  bushing 
in  the  socket,  and  above  the  point  where  the  cord  comes 
through  the  ceiling  block  or  rosette,  in  order  that  the  strain 
may  be  taken  from  the  joints  and  binding  screws. 

Special  ceiling  blocks  or  rosettes  which  facilitate  the 
fastening  of  cords  are  on  the  market  and  should  be  used.  In 
fastening  the  cord  to  sockets  the  end  of  the  cord  should  be 
soldered.  This  does  away  with  the  liability  of  stray  strands 
short  circuiting  on  the  shell  of  the  socket  and  also  affords  a 


LOW   POTENTIAL   SYSTEMS. 


167 


better  and  stronger  contact  under  the  binding  screws.  This 
soldering  is  best  done  by  dipping  the  ends  of  the  cord  in  melted 
solder.  If  a  blow  torch  is  used  the  small  wires  are  very  easily 
overheated  and  the  soldering  may  do  more  harm  than  good. 
It  is  also  well  to  tape  the  ends  of  cords,  leaving  only  just 
enough  bare  metal  to  go  under  the  binding  screws  ;  the  tape 
will  hold  the  end  of  the  braid  and  will  confine  any  ends  of  wires 
which  do  not  happen  to  come  under  the  binding  screws. 


29.    Arc  Lamps  on  Constant-Potential  Circuits. 

a.  Must  have  a  cut-out  (see  No.  17  a)  for  each  lamp  or 
each  series  of  lamps. 

The  branch  conductors  should  have  a  carrying  capacity 
about  50  per  cent,  in  excess  of  the  normal  current  required  by 
the  lamp  to  provide  for  heavy  current  required  when  lamp  is 
started  or  when  carbons  become  stuck  without  uverfusing  the 
wires. 

Figure  101  at  the  left  gives  a  diagram  of  a  constant  poten- 
tial arc  circuit  as  generally  used  at  present  for  enclosed  arc 
lamps.  Each  arc  lamp  of  this  kind  requires  a  pressure  of  110 


Figure  101 


volts.  A  steadying  resistance,  R,  is  always  placed  in  series 
with  constant  potential  lamps,  its  object  being  to  keep  down 
the  current  while  the  lamp  feeds.  During  the  short  time  that 
the  two  carbons  are  together,  the  resistance  of  the  lamp  is  so 
low  that  an  enormous  amount  of  current  would  flow  were  it 
not  for  this  resistance.  With  most  lamps  this  resistance  is 


168  MODERN   ELECTRICAL  CONSTRUCTION. 

now  installed  in  the  hood.  Since  the  rule  requires  a  carrying 
capacity  about  50  per  cent  in  excess  of  the  normal  current  for 
branch  conductors,  it  would  be  well  to  provide  this  also  for 
mains  in  such  cases  where  groups  of  arc  lamps  are  likely  to  be 
controlled  by  one  switch  and  used  together. 

Figure  101  at  the  right  shows  a  diagram  of  wiring  for  open 
arc  lamps.  Two  lamps  are  usually  run  in  series  on  110  volts 
together  with  a  steadying  resistance.  An  open  arc  does  not 
work  well  with  a  pressure  higher  than  about  45  volts. 

b.  Must  only  be  furnished  with  such  resistance  or  regula- 
tors as  are  enclosed  in  non-combustible  material,  such  resist- 
ances being  treated  as  sources  of  heat.     Incandescent   lamps 
must  not  be  used  for  this  purpose. 

c.  Must  be  supplied  with  globes  and  protected  by  spark 
arresters  and  wire  netting  around  the  globe,  as  in  the  case  of 
series  arc  lamps  (see  Nos.  19  and  58). 

Outside  arc  lamps  must  be  suspended  at  least  eight  feet 
above  sidewalks.  Inside  arc  lamps  must  be  placed  out  of  reach 
or  suitably  protected. 

30.  Economy  Coils. 

a.  Economy  and  compensator  coils  for  arc  lamps  must  be 
mounted  on  non-combustible,  non-absorptive  insulating  sup- 
ports, such  as  glass  or  porcelain,  allowing  an  air  space  of  at 
least  one  inch  between  frame  and  support,  and  must  in  gen- 
eral be  treated  as  sources  of  heat. 

31.  Decorative  Lighting  Systems. 

a.  Special  permission  may  be  given  in  writing  by  the 
Inspection  Department  having  jurisdiction  for  the  temporary 
installation  of  approved  Systems  of  Decorative  Lighting,  pro- 
vided the  difference  of  potential  between  the  wires  of  any 
circuit  shall  not  be  over  150  volts  and  also  provided  that  no 
group  of  lamps  requiring  more  than  1,320  watts  shall  be  de- 
pendent on  one  cut-out. 

No  "System  of  Decorative  Lighting"  to  be  allowed  under 
this  rule  which  is  not  listed  in  the  Supplement  to  the  National 
Electrical  Code  containing  list  of  approved  fittings. 


LOW   POTENTIAL   SYSTEMS.  169 

b.  Incandescent  lamps  connected  in  series  must  not  be 
used  for  decorative  purposes  inside  of  buildings  except  by 
special  permission  in  writing  from  the  Inspection  Department 
having  jurisdiction. 

32.  Car  Wiring. 

a.  Must  always  be  run  out  of  reach  of  the  passengers, 
and  must  have  an  approved  rubber  insulating  covering  (see 
No.  41). 

33.  Car  Houses. 

a.  The  trolley  wires  must  be  securely  supported  on  insu- 
lating hangers. 

b.  The  trolley  hangers  must  be  placed  at  such  a  distance 
apart  that,  in  case  of  a  break  in  the  trolley  wire,  contact  cannot 
be  made  with  the  floor. 

c.  Must  have  a  cut-out  switch  located  at  a  proper  place 
outside  of  the  building,  so  that  all  trolley  circuits  in  the  build- 
ing can  be  cut  out  at  one  point,  and  line  circuit-breakers  must 
be  installed,  so  that  when  this  cut-out  switch  is  open  the  trolley 
wire  will  be  dead  at  all  points  within  100  feet  of  the  building. 
The  current  must  be  cut  out  of  the  building  whenever  the 
latter  is  not  in  use  or  the  road  is  not  in  operation. 

d.  All  lamps  and  stationary  motors  must  be  installed  in 
such  a  way  that  one  main  switch  can  control  the  whole  of  each 
installation — lighting    or    power — independently    of    the    main 
feeder  switch.     No  portable  incandescent  lamps  or  twin  wire 
will  be  allowed,  except  that  portable  incandescent  lamps  may 
be  used  in  the  pits,  the  circuit  to  be  controlled  by  a  switch 
placed  outside  of  the  pit,  and  the  connections  to  be  made  by 
two    approved    rubber-covered    flexible    wires    (see    No.    41), 
properly  protected  against  mechanical  injury. 

e.  All  wiring  and  apparatus  must  be  installed  in  accord- 
ance with  rules  for  constant-potential  systems. 

f.  Must  not  have  any  system  of  feeder  distribution  cen- 
tering in  the  building. 

g.  The   rails  must  be  bonded  at  each  joint  with  a  con- 


170  MODERN   ELECTRICAL   CONSTRUCTION. 

ductor  having  a  carrying  capacity  not  less  than  that  of  a  No.  2 
B.  &  S.  gage  annealed  copper  wire. 

h.  Cars  must  not  be  left  with  the  trolley  in  electrical  con- 
nection with  the  trolley  wire. 

34.    Lighting  and  Power  from  Railway  Wires. 

a.  Mast  not  be  permitted,  under  any  pretence,  in  the  same 
circnit  with  trolley  wires  with  a  ground  return,  except  in 
railway  cars,  electric  car  houses  and  their  power  stations;  nor 
shall  the  same  dynamo  he  used  for  both  purposes. 


HIGH-POTENTIAL  SYSTEMS. 

550  TO  3,500  VOLTS. 

Any  circuit  attached  to  any  machine  or  combination  of  ma- 
chines which  develops  a  difference  of  potential,  between 
any  two  wires,  of  over  550  volts  and  less  than  3,500  volts, 
shall  be  considered  as  a  high-potential  circuit,  and  as 
coming  under  that  class,  unless  an  approved  transforming 
device  is  used,  which  cuts  the  difference  of  potential  down 
to  550  volts  or  less. 

35.    Wires. 

(Sec  also  Nos.  14,  15  and  16.) 

a.  Must  have  an  approved  rubber-insulating  covering  (see 
No.  41). 

b.  Must  be  always  in  plain  sight  and  never  encased,  except 
where   required  by  the   Inspection   Department  having  juris- 
diction. 

c.  Must  be  rigidly  supported  on  glass  or  porcelain  insula- 
tors, which  raise  the  wire  at  least  one  inch  from  the  surface 
wired  over,  and  must  be  kept  about  eight  inches  apart. 

Rigid  supporting  requires  under  ordinary  conditions,  where 
wiring  along  flat  surfaces,  supports  at  least  about  every  four 
and  one-half  feet.  If  the  wires  are  unusually  liable  to  be 
disturbed,  the  distance  between  supports  should  be  shortened. 

In  buildings  of  mill  construction,  mains  of  No.  8  B.  &  S. 
gage  or  over,  where  not  liable  to  be  disturbed,  may  be  separated 
about  ten  inches  and  run  from  timber  to  timber,  not  breaking 
around,  and  may  be  supported  at  each  timber  only. 


HIGH   POTENTIAL   SYSTEMS.  171 

d.  Must  be  protected  on  side  walls  from  mechanical 
injury  by  a  substantial  boxing,  retaining  an  air  space  of  one 
inch  around  the  conductors,  closed  at  the  top  (the  wires 
passing  through  bushed  holes)  and  extending  not  less  than 
seven  feet  from  the  floor.  When  crossing  floor  timbers,  in 
cellars,  or  in  rooms  where  they  might  be  exposed  to  injury, 
wires  must  be  attached  by  their  insulating  supports  to  the 
under  side  of  a  wooden  strip  not  less  than  one-half  an  inch  in 
thickness. 

For  general  suggestions  on  protection,  see  note  under 
No.  24  e.  See  also  note  under  No.  18  e. 

36.  Transformers.     (When   permitted   inside   buildings,   see 

No.  13.) 

(For  construction  rules,  sec  No.  62.) 
(Sec  also  Nos.  13  and  13  A.) 

Transformers  must  not  be  placed  inside  of  buildings  with- 
out special  permission  from  the  Inspection  Department  having 
jurisdiction. 

a.  Must   be   located   as   near   as  possible   to  the  point   at 
which  the  primary  wires  enter  the  building. 

b.  Must   be   placed   in    an   enclosure   constructed    of   fire- 
resisting  material ;  the  enclosure  to  be  used  only  for  this  pur- 
pose, and  to  be  kept  securely  locked,  and  access  to  the  same 
allowed  only  to  responsible  persons. 

c.  Must  be  effectually  insulated  from  the  ground,  and  the 
enclosure   in   which  they  are  placed  must  be  practically  air- 
tight, except  that  it  must  be  thoroughly  ventilated  to  the  out- 
door air,  if  possible,  through  a  chimney  or  flue.     There  should 
be  at  least  six  inches  air  space  on  all  sides  of  the  transformer. 

37.  Series  Lamps. 

a.  No  multiple  series  or  series  multiple  system  of  light- 
ing will  be  approved. 

b.  Must  not,  under  any  circumstances,  be  attached  to  gas 
fixtures. 


172  MODERN   ELECTRICAL  CONSTRUCTION. 

EXTRA-HIGH-POTENTIAL  SYSTEMS. 
OVER  3,500  VOLTS. 

Any  circuit  attached  to  any  machine  or  combination  of  ma- 
chines which  develops  a  difference  of  potential,  between 
any  two  wires,  of  over  3,500  volts,  shall  be  considered  as 
an  extra-high- potential  circuit,  and  as  coming  under  that 
class,  unless  an  approved  transforming  device  is  used, 
zvhich  cuts  the  difference  of  potential  down  to  3,500  -volts 
or  less. 

38.  Primary  Wires. 

a.  Must  not  be  brought  into  or  over  buildings,  except 
power  stations  and  sub-stations. 

39.  Secondary  Wires. 

a.  Must  be  installed  under  rules  for  high-potential  sys- 
tems when  their  immediate  primary  wires  carry  a  current  at  a 
potential  of  over  3,500  volts,  unless  the  primary  wires  are 
installed  in  accordance  with  the  requirements  as  given  in  rule 
12  A  or  are  entirely  underground,  within  city,  town  and  village 
limits. 


NOTICE— DO  NOT  FAIL  TO  SEE  WHETHER  ANY 
RULE  OR  ORDINANCE  OF  YOUR  CITY  CONFLICTS 
WITH  THESE  RULES. 


CLASS  D. 

FITTINGS,  MATERIALS  AND  DETAILS  OF 
CONSTRUCTION. 


ALL  SYSTEMS  AND  VOLTAGES. 
Insulated  Wires — Rules  40  to  48 

40.  General  Rules. 

a.  Copper    for   insulated   conductors   must  never   vary   in 
diameter  so  as  to  be  more  than  two  one-thousandths  of  an  inch 
less  than  the  specified  size. 

b.  Wires   and   cables   of  all   kinds  designed   to   meet   the 
following  specifications  must  be  plainly  tagged  or  marked  as 
follows : 

1.  The  maximum  voltage  at  which  the  wire  is  designed  to 
be  used. 

2.  The  words  "National  Electrical  Code  Standard." 

3.  Name  of  the  manufacturing  company  and,  if  desired, 
trade  name  of  the  wire. 

4.  Month  and  year  when  manufactured. 

It  Is  recommended  that  all  wires  complying  with  these 
specifications  be  provided  with  a  distinctive  marking  on  the 
insulation  or  braid  which  will  serve  to  identify  them  at  any 
time. 

41.  Rubber-Covered  Wire. 

a.     Copper  for  conductors  must  be  thoroughly  tinned. 


174  MODERN   ELECTRICAL  CONSTRUCTION. 

b.  Must  be  of  rubber  or  other  approved  substance,  and  of 

a  thickness  not  less  than  that  given  in  the  following  table :          \ 
B.  &  S.  Gage.  Thickness. 

18  to       16 ,..1-32  Inch. 

15  to         8 3-64      " 

7  to         2 1-16     " 

1  to  0000 5-64     " 

Circular  Mils. 

250,000  to      500,000 3-32     " 

500,000  to  1.000,000 7-64      " 

Over  1,000,000 .    1-8     " 

Measurements  of  insulating  wall  are  to  be  made  at  the 
thinnest  portion  of  the  dielectric. 

c.  The    completed   coverings    must    show    an    insulation 
resistance  of  at  least  100  megohms  per  mile  during  thirty  days' 
immersion  in  water  at  seventy  degrees  Fahrenheit. 

d.  Each    foot   of   the   completed   covering   must    show   a 
dielectric  strength  sufficient  to  resist  throughout  five  minutes 
the  application  of  an  electro-motive  force  of  3,000  volts  per 
one  sixty-fourth  of  an  inch  thickness  of  insulation  under  the 
following  conditions : 

The  source  of  alternating  electro-motive  force  shall  be  a 
transformer  of  at  least  one  kilowatt  capacity.  The  application 
of  the  electro-motive  force  shall  first  be  made  at  4,000  volts 
for  five  minutes  and  then  the  voltage  increased  by  steps  of  not 
over  3,000  volts,  each  held  for  five  minutes,  until  the  rupture 
of  the  insulation  occurs.  The  tests  for  dielectric  strength  shall 
be  made  on  a  sample  of  wire  which  has  been  immersed  in 
water  for  seventy-two  hours.  One  foot  of  the  wire  under 
test  is  to  be  submerged  in  a  conducting  liquid  held  in  a  metal 
trough,  one  of  the  transformer  terminals  being  connected  to 
the  copper  of  the  wire  and  the  other  to  the  metal  of  the  trough. 

Insulations  for  Voltages  between  600  and  3,500 

c.    The  thickness  of  the  insulating  wall  must  not  be  less 
than  that  given  in  the  following  table : 
B.  &  S.  Gage.  Thickness. 

14  to        1 3-32  inch. 

0  to  0000 3-32  inch,  covered  by  tape  or  braid. 

Circular  Mils. 

250,000   to  500,000 3-32  inch,  covered  by  tape  or  braid. 

Over  500,000 1-8  inch,  covered  by  tape  or  braid. 


FITTINGS,    MATERIALS,  ETC  175 

f.  The    requirements   as   to    insulation    and    break-down 
resistance  for  wires  for  low-potential  systems  shall  apply,  with 
the  exception  that  an  insulation  resistance  of  not  less  than  300 
megohms  per  mile  shall  be  required. 

Insulation  for  Voltage  over  3,500. 

g.  Wire  for  arc-light  circuits  exceeding  3,500  volts  poten- 
tial must  have  an  insulating  wall  not  less  than  three-sixteenths 
of  an  inch  in  thickness,  and  shall  withstand  a  breakdown  test 
of  at  least  30,000  volts  and  have  an  insulation  of  at  least  500 
megohms  per  mile. 

The  tests  on  this  wire  to  be  made  under  the  same  condi- 
tions as  for  low-potential  wires. 

Specifications  for  insulations  for  alternating  currents  ex 
ceeding  3,500  volts  have  been  considered,  but  on  account  of  the 
somewhat  complex  conditions  in  such  work,  it  has  so  far  been 
deemed  inexpedient  to  specify  general  insulations  for  this  use. 

Protecting  Braid. 

h.  All  of  the  above  insulations  must  be  protected  by  a 
substantial  braided  covering,  property  saturated  with  a  pre- 
servative compound.  This  covering  must  be  sufficiently  strong 
to  withstand  all  the  abrasion  likely  to  be  met  with  in  practice, 


Figure  103 

and  sufficiently  elastic  to  permit  all  wires  smaller  than  No.  7 
B.  &  S.  gage  to  be  bent  around  a  cylinder  with  twice  the 
diameter  of  wire,  without  injury  to  the  braid. 

42.     Slow-burning  Weatherproof  Wire. 

(See  Figure  103.) 

a.  The  insulation  must  consist  of  two  coatings,  one  to  be 
fireproof  in  character  and  the  other  to  be  weatherproof.  The 
fireproof  coating  must  be  on  the  outside  and  must  comprise 


176  MODERN   ELECTRICAL  CONSTRUCTION. 

about  six-tenths  of  the  total  thickness  of  the  wall.  The  com- 
pleted covering  must  be  of  a  thickness  not  less  than  that  given 
in  the  following  table: 

B.  &  S.  Gage.  Thickness. 

14  to         8 3-64  inch. 

7  to         2 1-16 

1  to  0000. 5-64 

Circular  Mils. 

250,000  to      500,000 3-32 

500,000  to  1,000,000 7-64 

Over  1,000,000 1-8 

Measurements  of  insulating  wall  are  to  be  made  at  the 
thinnest  portion  of  the  dielectric. 

This  wire  is  not  as  burnable  as  "weatherproof,"  nor  as  sub- 
ject to  softening  under  heat.  It  is  not  suitable  for  outside 
work. 

b.  The  fireproof  coating  shall  be  of  the  same  kind  as  that 
required  for  "slow-burning  wire,"  and  must  be  finished  with  a 
hard,  smooth  surface  if  it  is  on  the  outside. 

c.  The  weatherproof  coating  shall  consist  of  a  stout  braid, 
applied  and  treated  as  required  for  "weatherproof  wire,"  and 
must  be  thoroughly  slicked  down  if  it  is  on  the  outside. 

43.     Slow-burning  Wire. 

a.  "The  insulation  must  consist  of  layers  of  cotton  or 
other  thread,  all  the  interstices  of  which  must  be  filled  with  the 
fireproofing  compound,  or  of  material  having  equivalent  fire 


Figure  104 

resisting  and  insulating  properties.  The  outer  layer  must 
be  braided  and  specially  designed  to  withstand  abrasion.  The 
thickness  of  insulation  must  not  be  less  than  that  required  for 
slow-burning  weatherproof  wire  and  the  outer  surface  must  be 
finished  smooth  and  hard." 

"The  solid  constituent  of  the  fireproofing  compound  must 
not  be  susceptible  to  moisture,  and  must  not  burn  even  when 
ground  in  an  oxidizable  oil,  making  a  compound  which,  while 
proof  against  fire  and  moisture,  at  the  same  time  has  consider- 


FITTINGS,    MATERIALS,   ETC.  177 

able  elasticity,  and  which  when  dry  will  suffer  no  change  at  a 
temperature  cf  250°  F.,  and  which  will  not  burn  at  even  a 
higher  temperature. 

44.  Weatherproof  Wire. 

(Sec  Figure  104.) 

a.  The  insulating  covering  shall  consist  of  at  least  three 
braids,  all  of  which  must  be  thoroughly  saturated  with  a  dense 
moisture-proof  compound,  applied  in  such  a  manner  as  to 
drive  any  atmospheric  moisture  from  the  cotton  braiding, 
thereby  securing  a  covering  to  a  great  degree  waterproof  and 
of  high  insulating  power.  This  compound  must  retain  its 
elasticity  at  0  deg.  Fahr.  and  must  not  drip  at  160  deg.  Fahr. 
The  thickness  of  insulation  must  not  be  less  than  that  required 
for  "slow-burning  weatherproof  wire,"  and  the  outer  surface 
must  be  thoroughly  slicked  down. 

This  wire  Is  for  use  outdoors,  where  moisture  is  certain  and 
where  fireproof  qualities  are  not  necessary. 

45.  Flexible  Cord. 

(For  installation  rules,  sec  No.  28.) 

a.  Must  be  made  of  stranded  copper  conductors,  each 
strand  to  be  not  larger  than  No.  26  or  smaller  than  No.  30 


Figure  105 

B.  &  S.  gage,  and  each  stranded  conductor  must  be  covered 
by  an  approved  insulation  and  protected  from  mechanical 
injury  by  a  tough,  braided  outer  covering. 

For  Pendant  Lamps. 

(See   Figure   105.) 

In  this  class  Is  to  be  included  all  flexible  cord  which,  under 
usual  conditions,  hangs  freely  in  air,  and  which  is  not  likely 
to  be  moved  sufficiently  to  ccme  in  contact  with  surrounding 
objects. 

It  should  be  noted  that  pendant  lamps  provided  with  long 
cords,  so  that  they  can  be  carried  about  or  hung  over  nails  or 


178  MODERN   ELECTRICAL  CONSTRUCTION. 

on  machinery,  etc.,  are  not  included  in  this  class,  even  though 
they  are  usually  allowed  to  hang  freely  in  air. 

b.  Each  stranded  conductor  must  have  a  carrying  capacity 
equivalent  to  not  less  than  a  No.  18  B.  &  S.  gage  wire. 

c.  The  covering  of  each  stranded  conductor  must  be  made 
up  as  follows : 

1.  A  tight,  close  wind  of  fine  cotton. 

2.  The  insulation  proper,  which  shall  be  waterproof. 

3.  An  outer  cover  of  silk  or  cotton. 

The  wind  of  cotton  tends  to  prevent  a  broken  strand  punc- 
turing the  insulation  and  causing  a  short  circuit.  It  also  keeps 
the  rubber  from  corroding  the  copper. 

d.  The  insulation  must  be  solid,  at  least  one  thirty-second 
of  an  inch  thick,  and  must  show  an  insulation  resistance  of 
fifty  megohms  per  mile  throughout  two  weeks'  immersion  in 
water  at  70  degrees  Fahrenheit,  and  stand  the  tests  prescribed 
for  low-tension  wires  as  far  as  they  apply. 

c.  The  outer  protecting  braiding  should  be  so  put  on  and 
sealed  in  place  that  when  cut  it  will  not  fray  out,  and  where 
cotton  is  used,  it  should  be  impregnated  with  a  flameproof 
paint,  which  will  not  have  an  injurious  effect  on  the  insulation. 

For  Portables. 

(See  Figure  zoo".) 

In  this  class  is  included  all  cord  used  on  portable  lamps, 
small  portable  motors,  or  any  device  which  is  liable  to  be 
carried  about. 

f.  Flexible  cord  for  portable  use  must  meet  all  of  the 
requirements  for  flexible  cord  "for  pendant  lamps,"  both  as  to 


Figure  106 

construction  and  thickness  of  insulation,  and  in  addition  must 
have  a  tough  braided  cover  over  the  whole.  There  must  also 
be  an  extra  layer  of  rubber  between  the  outer  cover  and  the 
flexible  cord,  and  in  most  places  the  outer  cover  must  be  sat- 
urated with  a  moisture-proof  compound,  thoroughly  slicked 
down,  as  required  for  "weatherproof  wire"  in  No.  44.  In 


FITTINGS,    MATERIALS,  ETC.  179 

offices,  dwellings  or  in  similar  places  where  the  appearance  is 
an  essential  feature,  a  silk  cover  may  be  substituted  for  the 
weatherproof  braid. 

For  Portable  Heating  Purposes. 

(Sec  Figure  107.) 

g.     Must  be  made  up  as  follows : 

1.  A  tight,  close  wind  of  fine  cotton. 

2.  A   thin    layer   of   rubber   or  other   cementing  material 
about  one  one-hundreth  of  an  inch  thick. 


Figure  107 

3.  A    layer    of    asbestos    insulation    at    least    three    sixty- 
fourths  of  an  inch  thick. 

4.  A  stout  braid  of  cotton. 

5.  An  outer  reinforcing  cover  especially  designed  to  with- 
stand abrasion. 

This  cord  is  in  no  sense  waterproof,  the  thin  layer  of  rubber 
being  intended  merely  to  serve  as  a  seal  to  help  hold  in  place 
the  fine  cotton  and  asbestos,  and  it  should  be  put  on  in  such  a 
way  as  will  accomplish  this. 

46.     Fixture  Wire. 

(Sec  Figure  108.) 

(For  installation  rules,  sec  No.  24  v  to  y.) 

a  May  be  made  of  solid  or  stranded  conductors,  with  no 
strands  smaller  than  No.  30  B.  &  S.  gage,  and  must  hai~e  a 
carrying  capacity  not  less  than  that  of  a  No.  18  B.  &  S.  gage 
wire. 

b.  Solid  conductors  must  be  thoroughly  tinned.  If  a 
stranded  conductor  is  used,  it  must  be  covered  by  a  tight,  close 
wind  of  fine  cotton. 

r.  Must  have  a  solid  rubber  insulation  of  a  thickness  not 
less  than  one  thirty-second  of  an  inch  for  Nos.  18  to  16  B.  &  S. 


180  MODERN   ELECTRICAL  CONSTRUCTION. 

gage,  and  three  sixty-fourths  of  an  inch  for  Nos.  14  to  8  B.  & 
S.  gage,  except  that  in  arms  of  fixtures  not  exceeding  twenty- 
four  inches  in  length  and  used  to  supply  not  more  than  one 
sixteen-candle-power  lamp  or  its  equivalent,  which  are  so  con- 


Figure  108 

structed  as  to  render  impracticable  the  use  of  a  wire  with  one 
thirty-second  of  an  inch  thickness  of  rubber  insulation,  a 
thickness  of  one  sixty-fourth  of  an  inch  will  be  permitted. 

d.  Must  be  protected  with  a  covering  at  least  one  sixty- 
fourth  of  an  inch  in  thickness,  sufficiently  tenacious  to  with- 
stand the  abrasion  cf  being  pulled  into  the  fixture,    and  suf- 
ficiently elastic  to  permit  the  wire  to  be  bent  around  a  cylinder 
with  twice  the  diameter  of  the  wire  without  injury  to  the  braid. 

e.  Must  successfully  withstand  the  tests  specified  in  Nos. 
41  c  and  41  d. 

47.     Conduit  Wire. 

(For  installation  rules,  see  No.  24  n  to  p.) 

a.  Single  wire  for  lined  conduits  must  comply  with  the 
requirements  of  No.  41  (Figure  109).  For  unlined  conduits 
it  must  comply  with  the  same  requirements — except  that  tape 


Figure  109  Figure  110  Figure  111 

may  be  substituted  for  braid — and  in  addition  there  must  be 
a  second  outer  fibrous  covering,  at  least  one  thirty-second  of 
an  inch  in  thickness  and  sufficiently  tenacious  to  withstand  the 
abrasion  of  being  hauled  through  the  metal  conduit.  (Figures 
110  and  111). 

b.  For  twin  or  duplex  wires  in  lined  conduit,  each  con- 
ductor must  comply  with  the  requirements  of  No.  41 — except 
that  tape  may  be  substituted  for  braid  on  the  separate  con- 


FITTINGS,   MATERIALS,  ETC  181 

ductors — and  must  have  a  substantial  braid  covering  the  whole. 
For  unlined  conduit,  each  conductor  must  comply  with  require- 
ments of  No.  41 — except  that  tape  may  be  substituted  for  braid 
— and  in  addition  must  have  a  braid  covering  the  whole,  at 
least  one  thirty-second  of  an  inch  in  thickness  and  sufficiently 
tenacious  to  withstand  the  abrasion  of  being  hauled  through 
the  metal  conduit  (Figure  112). 

c.  For  concentric  wire,  the  inner  conductor  must  comply 
with  the  requirements  of  No.  41 — except  that  tape  may  be 
substituted  for  braid — and  there  must  be  outside  of  the  outer 
conductor  the  same  insulation  as  on  the  inner,  the  whole  to  be 


Figure  112  Figure  113 

covered  with  a  substantial  braid,  which  for  unlined  conduits 
must  be  at  least  one  thirty-second  of  an  inch  in  thickness,  and 
sufficiently  tenacious  to  withstand  the  abrasion  of  being  hauled 
through  the  metal  conduit  (Figure  113). 

The  braid  or  tape  required  around  each  conductor  in  duplex, 
twin  and  concentric  cables  is  to  hold  the  rubber  insulation  in 
place  and  prevent  jamming  and  flattening. 

48.    Armored  Cable. 

(Sec  Figure  114.) 

a.  The  armor  of  such  cables  must  have  at  least  as  great 
strength  to  resist  penetration  of  nails,  etc.,  as  is  required  for 


Figure  114 

metal  conduits  (see  No.  49  &),  and  its  thickness  must  not  be 
less  than  that  specified  in  the  following  table : 


182  MODERN   ELECTRICAL  CONSTRUCTION. 

Nominal 

Internal 

Diameter. 

Inches. 


Actual 

Actual 

Internal 

External 

Thickness 

Diameter. 

Diameter 

of  Wall. 

Inches. 

Inches. 

Inches. 

.27 

.40 

.06 

.36 

.54 

.08 

.49 

.67 

.09  ' 

.62 

.84 

.10 

.82 

1.05 

.11 

1.04 

1.31 

.13 

1.38 

1.66 

.14 

1.61 

1.90 

.14 

2.06 

2.37 

.15 

2.46 

2.87 

.20 

3.06 

3.50 

.21 

3.54 

4.00 

.22 

4.02 

4.50 

.23 

4.50 

5.00 

.24 

5.04 

5.56 

.25 

6.06 

6.62 

.28 

An  allowance  of  two  one-hundredths  of  an  Inch  for  variation 
in  manufacturing  and  loss  of  thickness  by  cleaning  will  be 
permitted. 

b.  The  conductors  in  same,  single  wire  or  twin  conductors, 
must  have  an  insulating  covering  as  required  by  No.  41 ;  if 
any  filler  is  used  to  secure  a  round  exterior,  it  must  be  impreg- 
nated with  a  moisture  repellent,  and  the  whole  bunch  of  con- 
ductors and  fillers  must  have  a  separate  exterior  covering. 

49.    Interior  Conduits. 

(For  installation  rules,  see  Nos.  24  n  to  p  and  25.) 

a.  Each  length  of  conduit,  whether  lined  or  unlined,  must 
have  the  maker's  name  or  initials  stamped   in  the  metal   or 
attached  thereto  in  a  satisfactory  manner,  so  that  inspectors 
can  readily  see  the  same. 

The  use  of  paper  stickers  or  tags  cannot  be  considered  satis- 
factory methods  of  marking-,  as  they  are  readily  loosened  and 
lost  off  in  the  ordinary  handling  of  the  conduit. 

Metal  Conduits  with  Lining  of  Insulating  Material. 
(Sec  Figure  1/5.) 

b.  The  metal  covering  or  pipe  must  be  at  least  as  strong 
as  the  ordinary  commercial  forms  of  gas  pipe  of  the  same 
size,  and  its  thickness  must  be  not  less  than  that  of  standard 
gas  pipe  as  specified  in  the  table  given  in  No.  48. 

c.  Must  not  be   seriously  affected  externally  by  burning 


FITTINGS,   MATERIALS,  ETC.  183 

out  a  wire  inside  the  tube  when  the  iron  pipe  is  connected  to 
one  side  of  the  circuit. 

d.  Must  have  the  insulating  lining  firmly  secured  to  the 
pipe. 

c.  The  insulating  lining  must  not  crack  or  break  when  a 
length  of  the  conduit  is  uniformly  bent  at  temperature  of  212 
degrees  Fahrenheit  to  an  angle  of  ninety  degrees,  with  a  curve 


Figure    115 

having  a  radius  of  fifteen  inches,  for  pipes  of  one  inch  and  less, 
and  fifteen  .times  the  diameter  of  pipe  for  larger  sizes. 

/.  The  insulating  lining  must  not  soften  injuriously  at  a 
temperature  below  212  degrees  Fahrenheit  and  must  leave 
water  in  which  it  is  boiled  practically  neutral. 

g.  The  insulating  lining  must  be  at  least  one  thirty-second 
of  an  inch  in  thickness.  The  materials  of  which  it  is  com- 
posed must  be  of  such  a  nature  as  will  not  have  a  deteriorating 
effect  on  the  insulation  of  the  conductor  and  be  sufficiently 
tough  and  tenacious  to  withstand  the  abrasion  test  of  drawing 
long  lengths  of  conductors  in  and  out  of  same. 

h.  The  insulating  lining  must  n^t  be  mechanically  weak 
after  three  days'  submersion  in  water,  and  when  removed 
from/the  pipe  entire,  must  not  absorb  more  than  ten  per  cent 
of  its  weight  of  water  during  100  hours  of  submersion. 

"/.'"  All  elbows  or  bends  must  be  so  made, that  the  con- 
duit or  lining  of  same  will  hot  be  injured.  The'. radius  of. the 
curve  of  the 'inner  edge  of  any  elbow  must  not  be  less  than 
three 'and  one-half  inches. 

Unlined  Metal  Conduits. 

(Sec  Figure  116.) 

j.  Plain  iron  or  steel  pipes  of  thickness  and  strengths 
equal  to  those  specified  for  lined  conduits  in  No.  49  b  may  be 


184  MODERN   ELECTRICAL  CONSTRUCTION. 

used  as  conduits,  provided  their  interior  surfaces  are  smooth 
and  free  from  burs.  In  order  to  prevent  oxidation,  the  pipe 
must  be  galvanized,  or  the  interior  surfaces  coated  or  en- 


Figure  116 

ameled  with  some  substance  which  will  not  soften  so  as  to 
become  sticky  and  prevent  the  wire  from  being  withdrawn 
from  the  pipe. 

k.  All  elbows  or  bends  must  be  so  made  that  the  conduit 
will  not  be  injured.  The  radius  of  the  curve  of  the  inner  edge 
of  any  elbow  not  to  be  less  than  three  and  one-half  inches. 

Outlet  Boxes. 

(Sec  Figure   7/7.) 

/.  Must  be  of  pressed  steel  having  a  wall  thickness  not 
less  than  .081  in.  (No.  12  B.  &  S.  gage)  or  of  cast  metal  hav- 


Figure  117 

ing  a.  wall  thickness  not  less  than  0.128  in.    (No.  8  B.  &  S. 
gage). 

m.     Must  be  well  galvanized,  enameled  or  otherwise  coated, 
inside  and  out,  to  pi  event  oxidation. 


FITTINGS,    MATERIALS,   ETC 


185 


«.  Inlet  holes  must  be  effectually  closed  when  not  in 
use  by  metal  which  will  afford  protection  substantially  equiv- 
alent to  that  of  the  walls  of  the  box. 

o.  Must  be  plainly  marked  where  it  will  be  seen  when 
installed  with  the  name  or  trade  mark  of  the  manufacturer. 

/>.  Boxes  used  with  lined  conduit  must  comply  with  the 
foregoing  and  in  addition  must  have  a  tough  and  tenacious 
insulating  lining  firmly  secured  in  position. 

50.    Wooden  Mouldings. 

(Sec  Figure  118.) 
(For  wiring  rules,  sec  No.  24,  I  and  m.) 

a.  Must  have,  both  outside  and  inside,  at  least  two  coats 
of  waterproof  material,  or  be   impregnated   with   a   moisture 
repellent. 

b.  Must  be  made  in  two  pieces,  a  backing  and  a  capping, 
and  must  afford  suitable  protection  from  abrasion.     Must  be 
so  constructed  as  to  thoroughly  encase  the  wire  and  provide 


Figure  118 


a  one-half  inch  tongue  between  the  conductors  and  a  solid 
backing,  which,  under  grooves,  shall  not  be  less  than  three- 
eighths  of  an  inch  in  thickness. 

It  is  recommended  that  only  hardwood  moulding  be  used. 

50A.    Tubes  and  Bushings. 

(See  Figure  118.) 
a.     Construction. — Must  be  made  straight  and  free  from 


186  MODERN    ELECTRICAL   CONSTRUCTION. 

checks  or  rough  projections,  with  ends  smooth  and  rounded 
to  facilitate  the  drawing  in  of  the  wire  and  prevent  abrasion 
of  its  covering. 

b.  Material  and  Test. — Must  be  made  of  non-combustible 
insulating  material,   which,  when  broken  and   submerged   for 
100  hours  in  pure  water  at  70  degrees   Fahrenheit,  will  not 
absorb  over  one-half  of  one  per  cenf  of  its  weight. 

c.  Marking. — Must  have  the  name,  initials,  or  trade  mark 
of  the  manufacturer  stamped  in  the  ware. 

d.  Sizes. — Dimensions   of   walls    and    heads   must   be    at 
least  as  great  as  those  given  in  the  following  table : 

Diameter  External  Thick-  External  Length 

Of  Diameter.  ness  of  Diameter  of 

Hole.  Wall.  of  Head.  Head. 

Inches.  Inches.  Inches.  Inches.  Inches. 

5/16  9/16  %                    13/16  % 

%  11/16  5/32                     15/16  % 

%  13/16  5/32                1     3/16  % 

%  15/16  5/32                 1      5/16  % 

%  1      3/16  7/32                 1   11/16  % 

1  1      7/16  7/32                 1   15/16  % 
IU  1   13/16  9/32                 2     5/16  % 
1%  2      3/16  11/32                 2   11/16  % 
1%  2     9/16  13/32                3      1/16  % 

2  2  15/16  15/32                 3     7/16  % 
2%  3      5/16  17/32                 3   13/16  1 
2%  3-11/16  19/32                 4     3/16  1 

An  allowance  of  one-sixty-fourth  of  an  inch  for  variation 
in  manufacturing  will  be  permitted,  except  in  the  thickness  of 
the  wall. 

SOB.     Cleats. 

(See  Figure  118.) 

a.  Construction. — Must    hold    the    wire    firmly    in    place 
without  injury  to  its  covering. 

Sharp  edges  which  may  cut  the  wire  should  be  avoided. 

b.  Supports. — Bearing    points    on    the    surface    must    be 
made  by  ridges  or  rings  about  the  holes  for  supporting  screws, 
in  order  to  avoid  cracking  and  breaking  when  screwed  tight. 

c.  Material  and  Test. — Must  be  made  of  non-combustible 
insulating  material,  which,  when  broken  and  submerged   for 


FITTINGS,   MATERIALS,  ETC.  187 

100  hours   in  pure  water  at  70  degrees   Fahrenheit,  will  not 
absorb  over  one-half  of  one  per  cent  of  its  weight. 

d.  Marking. — Must  have  the  name,  initials  or  trademark 
of  the  manufacturer  stamped  in  the  ware. 

c.  Sizes. — Must  conform  to  the  spacings  given  in  the  fol- 
lowing table: — 

Distance  from  Wire  Distance  between 

Voltage.  to  Surface.  Wires. 

0-300  Va  inch.  2^  inches. 

This  rule  will  not  be  interpreted  to  forbid  the  placing  of  the 
neutral  of  an  Edison  three-wire  system  in  the  conter  of  the 
three-wire  cleat  where  the  difference  of  potential  between  the 
outside  wirer.  is  not  over  300  volts,  provided  the  outside  wires 
are  separated  two  and  one-half  inches. 

50  C.     Flexible  Tubing. 

(Sec  Figure  119.} 

The  following  specifications  are  designed  to  cover  the 
construction  of  flexible  tubes  for  fished  v.-ork,  loop  system  and 
for  mechanical  protection  to  wires  where  not  exposed  to 
moisture. 

Tubes  complying  with  these  requirements  must  not  be  used 
for  a  conduit  system  of  wiring. 

a.  Must  be  constructed  to  meet  the  following  require- 
ments : 

Must    have    a    sufficiently    smooth    interior    surface    to 
allow  the  ready  introduction  of  the  wire. 

Must  be  constructed  of  or  treated  with  materials  which 
will  serve  as  moisture  repellants. 


Figure  119 


Must  have  a  substantial  outer  covering  especially  de- 
signed to  withstand  abrasion. 

b.     The  linings  must  be  secured  in  position  so  that  they 
cannot  be  readily  removed. 


188  MODERN   ELECTRICAL  CONSTRUCTION. 

c.  The  tube  must  be  thoroughly  flexible  at  all  temperatures 
at  which  it  is  to  be  used. 

d.  Must  not  crack  or  break  when  kinked  or  flattened  out. 
c.     Must  be  sufficiently  tough  and  tenacious  to  withstand 

severe  tension  without  injury;  the  interior  diameter  must  not 
be  diminished  or  the  tube  opened  up  at  any  point  by  the  appli- 
cation of  a  reasonable  stretching  force. 

/.  Must  not  close  to  prevent  the  insertion  of  the  wire 
after  the  tube  has  been  kinked  and  straightened  out,  or 
flattened. 

g.  Must  not  soften  injuriously,  or  cause  the  wire  to  stick 
within  the  tube  when  subjected  to  a  temperature  of  150  degrees 
Fahrenheit. 

51.    Switches. 

(For  installation  rules,  see  Nos.  17  and  22.) 
General   Rules. 

a.  Must,  when  used  for  service  switches,  indicate,  on  in- 
spection, whether  the  current  be  "on"  or  "off." 

b.  Must,  for  constant-current  systems,  close  the  main  cir- 
cuit and  disconnect  the  branch  wires  when  turned  "off" ;  must 
be  so  constructed  that  they  shall  be  automatic  in  action,  not 
stopping  between  points  when  started,  and  must  prevent  an 
arc  between  the  points  under  all  circumstances.     They  must 
indicate  whether  the  current  be  "on"  or  "off." 

Knife  Switches 

(See  Figure  120.) 

Knife  switches  must  be  made  to  comply  with  the  following 
specifications,  except  in  those  few  cases  where  peculiar  design 
allows  the  switch  to  fulfill  the  general  requirements  in  some 
other  way,  and  where  it  can  successfully  withstand  the  test 
of  Section  i.  In  such  cases,  the  switch  should  be  submitted 
for  special  examination  befcre  being  used. 


FITTINGS,    MATERIALS,  ETC. 


189 


c.  Base. — Must  be  mounted  on  non-combustible,  non-ab- 
sorptive, insulating  bases,  such  as  slate  or  por- 
celain. Bases  with  an  area  of  over  twenty-five 
square  inches  must  have  at  least  four  sup- 
porting screws.  Holes  for  the  supporting 
screws  must  be  so  located  or  countersunk  that 
there  will  be  at  least  one-half  inch  space,  meas- 
ured over  the  surface,  between  the  head  of 
the  screw  or  washer  and  the  nearest  live  metal 
part,  and  in  all  cases  when  between  parts  of 
opposite  polarity  must  be  countersunk. 

d.     Mounting. — Pieces    carrying    the    con- 
tact jaws  and  hir.gc  clips  must"  be  secured  to 
the  base  by  at  least  two  screws,  or  else  made 
with  a  square  shoulder  or  provided  with  dowel- 
pins,  to  prevent  possible  turnings,  and  the  nuts 
big.  120         or  screw-heads  on  the  under  side  of  the  base 
must  be  countersunk  not  less  than  one-eighth 
inch  and  covered  with  a  waterproof  compound  which  will  not 
melt  below  150  degrees  Fahrenheit. 

c.  Hinges. — Hinges  of  knife  switches  must  not  be  used 
to  carry  current  unless  they  are  equipped  with  spring  washers, 
held  by  lock-nuts  or  pins,  so  arranged  tha_t  a  firm  and  secure 
connection  will  be  maintained  at  all  positions  of  the  switch 
blades. 

Spring  washers  must  be  of  sufficient  strength  to  take  up 
any  wear  in  the  hinge  and  maintain  a  good  contact  at  all 
times. 

/.  Metal. — All  switches  must  have  ample  metal  for  stiff- 
ness and  to  prevent  rise  in  temperature  of  any  part  of  over 
fifty  degrees  Fahrenheit  at  full  load,  the  contacts  being  ar- 
ranged so  that  a  'thoroughly  good  bearing  at  every  point  is 
obtained  with  contact  surfaces  advised  for  pure  copper  blades 
of  about  one  square  inch  for  each  seventy-five  amperes ;  the 
whole  device  must  be  mechanically  well  made  throughout. 

g.  Cross-Bars. — All  cross-bars  less  than  three  inches  in 
length  must  be  made  of  insulating  material.  Bars  of  three 
inches  and  over,  which  are  made  of  metal,  to  insure  greater 
mechanical  strength,  must  be  sufficiently  separated  from  the 
jaws  of  the  switch  to  prevent  arcs  following  from  the  con- 


190  MODERN   ELECTRICAL   CONSTRUCTION. 

tacts  to  the  bar  on  the  opening  of  the  switch  under  any  cir- 
cumstances. Metal  bars  should  preferably  be  covered  with 
insulating  material. 

To  prevent  possible  turning  or  twisting  the  cross-bar  must 
be  secured  to  each  blade  by  two  screws,  or  the  joints  made 
with  square  shoulders  or  provided  with  dowel-pins. 

h.  Connections.  —  Switches  for  currents  of  over  twenty- 
five  amperes  must  be  equipped  with  lugs,  firmly-  screwed  of 
bolted  to  the  switch,  and  into  which  the  conducting  wires  shall 
be  soldered.  For  the  smaller  sized  switches  simple  clamps 
can  be  employed,  provided  they  are  heavy  enough  to  stand 
considerable  hard  usage. 

Where  lugs  are  not  provided,  a  rugged  double  V  groove 
clamp  is  advised.  A  set  screw  gives  a  contact  at  only  one 
point  is  more  likely  to  become  loosened,  and  is  almost  sure  to 
cut  into  .the  wire.  For  the  smaller  sizes,  a  screw  and  washer 
connection  with  turned-up  lugs  on  the  switch  terminal  gives  a 
satisfactory  contact. 

i.  Test.  —  Must  operate  successfully  at  50  per  cent  over- 
load in  amperes  and  25  per  cent  excess  voltage,  under  the  most 
severe  conditions  with  which  they  are  liable  to  meet  in  practice. 

This  test  is  designed  to  give  a  reasonable  margin  between 
the  ordinary  rating  of  the  switch  and  the  breaking-down  point 
thus  securing  a  switch  which  can  always  safely  handle  its  nor- 
mal load.  Moreover,  there  is  enough  leeway  so  that  a  nimh-nite 
amount  of  overloading  would  not  injure  the  switch. 

j.  Marking.  —  Must  be  plainly  marked  where  it  will  be 
visible,  when  the  switch  is  installed,  with  the  name  of  the 
maker  and  the  current  and  the  voltage  for  which  the  switch 
is  designed. 

k.  Spacings.  —  Spacings  must  be  at  least  as  great  as  those 
given  in  the  following  table.  The  spacings  specified  are  correct 
for  switches  to  be  used  on  direct-current  systems,  and  can 
therefore  be  safely  followed  in  devices  designed  for  alternating 
currents. 

125  volts  or  less: 

Minimum  Separation  of  Minimum 

Nearest  Metal  Parts  of  Break- 

Opposite  Polarity.  Distance. 
For  Switchboards  and  Panel  Boards  — 

10    amperes    or   less  ..........      %  inch.  *&  inch. 

11-25  amperes    ..............    1          "  % 


26-50 


FITTINGS,   MATERIALS,  ETC.  191 

For  Individual  Switches — 

10   amperes   or   less 1  inch.  %  inch. 

11-35  .  .  1  *4      **  1 

36-100         "  .  IV,      "  114 

101-300         "  .  .• 21/i      "  2 

301-600        "          2%  "  2% 

601-1000  3          "  2% 

126  to  250  volts: 
For  all  Switches — 

10   amperes   or    less 1%  inch.  1*4 

11-35   amperes    1%  "  \y2 

36-100         "  2Vi  "  2 

101-300          "  2%  "  214 

301-600         "  .2%  "  2% 

601-1000      "  3  "  2% 

For  100  ampere  switches  and  larger  the  above  spacings  for 

250  volts  direct  current  'are  also  approved  for  440  volts  alter- 
nating current.      Switches  with  these  sparings  intended  for  use 
en   alternating-current   systems   with    voltage  above   250    volts 
must  be  stamped  with  the  voltage  for  which  they  are  designed, 
followed  by  the  letters  "A,  C." 

251  to  600  volts: 

For  all  Switches — 

10   amperes   or   less 3  V^  inch.  3      inch. 

11-35  amperes    4         "  31/.      " 

36-100         "  4'/6      "  4          " 

Auxiliary  breaks  or  the  equivalent  are  recommended  for 
switches  designed  for  over  300  volts  and  less  than  100  amperes, 
and  will  be  required  on  switches  designed  for  use  in  breaking 
currents  greater  than  100  amperes  at  a  pressure  of  more  than 
300  volts. 

For  three-wire  Edison  systems  the  separations  and  break 
distances  for.  plain  three-pole  knife  switches  must  not  be  less 
than  those  required  in  the  above  table  for  switches  designed 
for  the  voltage  between  the  neutral  and  outside  wires. 


Snap  Switches. 

(See  Figures  121  and  122.) 

Flush,  push-button,  door,  fixture,  and  other  snap  switches 
used  on  constant-potential  systems,  must  be  constructed  in 
accordance  with  the  following  specifications. 

/.  Base. — Current-carrying  parts  must  be  mounted  on  non- 
combustible,  non-absorptive  insulating  bases,  such  as  slate  or 
porcelain,  and  the  holes  for  supporting  screws  should  be  coun- 
tersunk not  less  than  one-eighth  of  an  inch.  There  must 


192 


MODERN   ELECTRICAL  CONSTRUCTION. 


in  no  case  be  less  than  three  sixty-fourths  of  an  inch  space 
between  supporting  screws  and  current-carrying  parts. 

Sub-bases  of  non-combustible,     non-absorptive     insulating 
material,   which  will   separate  the   wires  at   least  one-half  of 


Figure  121 

an  inch  from  the  surface  wired  over,  must  be  ftirnished  with 
all  snap  switches  used  in  exposed  knob  or  cleat  work. 

m.  Mounting. — Pieces  carrying  contact  jaws  must  be  se- 
cured to  the  base  by  at  least  two  screws,  or  else  made  with 
a  square  shoulder,  or  provided  with  dowel-pins  or  otherwise 
arranged,  to  prevent  possible  turnings;  and  the  nuts  or  screw 
heads  on  the  under  side  of  the  base  must  be  countersunk  not 
less  than  one-eighth  inch,  and  covered  with  a  waterproof 
compound  which  will  not  melt  below  150  degrees  Fahrenheit. 

11.  Metal. — All  switches  must  have  ample  metal  for  stiff- 
ness and  to  prevent  rise  in  temperature  of  any  part  of  over 


Figure  122 

50  degrees  Fahrenheit  at  full  load,  the  contacts  being  arranged 
so  that  a  thoroughly  good  bearing  at  every  point  is  obtained. 
The  whole  device  must  be  mechanically  well  made  throughout. 


FITTINGS,   MATERIALS,  ETC.  193 

In  order  to  meet  the  above  requirements  on  temperature 
rise  without  causing  excessive  friction  and  wear  on  current- 
carrying  parts,  contact  surfaces  of  from  0.1  to  0.15  square  inch 
tor  each  10  amperes  will  be  required,  depending  upon  the  metal 
used  and  the  form  of  construction  adopted. 

o.  Insulating  Material. — Any  material  used  for  insulating 
current-carrying  parts  must  retain  its  .insulating  and  mechani- 
cal strength  when  subject  to  continued  use,  and  must  not 
soften  at  a  temperature  of  212  degrees  Fahrenheit. 

/>.  Binding  Posts. — Binding  posts  must  be  substantially 
made,  and  the  screws  must  be  of  such  size  that  the  threads 
will  not  strip  when  set  up  tight. 

q.  Covers. — Covers  made  of  conducting  material,  except 
face  plates  for  flush  switches,  must  be  lined  on  sides  and  top 
with  insulating,  tough  and  tenacious  material  at  least  one- 
thirty-second  inch  in  thickness,  firmly  secured  so  that  it  will 
not  fall  out  with  ordinary  handling.  The  side  lining  must  ex- 
tend slightly  beyond  the  lower  edge  of  the  cover. 

r.  Handle  or  Button. — The  handle  or  button  or  any  ex- 
posed parts  must  not  be  in  electrical  connection  with  the  cir- 
cuit. 

s.  Test. — Must  "make"  and  "break"  with  a  quick  snap, 
and  must  not  stop  when  motion  has  once  been  imparted  by  the 
button  or  handle. 

Must  operate  successfully  at  50  per  cent  overload  in  am- 
peres and  25  per  cent  excess  voltage,  under  the  most  severe 
conditions  with  which  they  are  liable  to  meet  in  practice. 

When  slowly  turned  "on  and  off"  at  the  rate  of  about  two  or 
three  times  per  minute,  while  carrying  the  rated  current,  must 
"make  and  break"  the  circuit  six  thousand  times  before 
failing. 

t.  Marking. — Must  be  plainly  marked,  where  it  may  be 
readily  seen  after  the  device  is  installed,  with  the  name  or 
trade  mark  of  the  maker  and  the  current  and  voltage  for 
which  the  switch  is  designed. 

On  flush  switches  these  markings  may  be  placed  on  the 
back  of  the  face  plate  or  on  the  sub-plate.  On  other  types 
they  must  be  placed  on  the  front  of  the  cap,  cover,  or  plate. 

Switches  which  indicate  whether  the  current  is  on  or 
"off"  are  recommended. 


194  MODERN   ELECTRICAL  CONSTRUCTION. 

52.    Cut-Outs  and  Circuit-Breakers. 

(Sec  Figure  123.) 

(For  installation  rules,  sec  Nos.  17  and  <?/.) 
General  Rules. 

a.  Must  be  supported  on  bases  of  non-combustible,  non- 
absorptive  insulating  material. 

b.  Cut-outs  must  be  of  plug  or  cartridge  type,  when  not 
arranged  in  approved  cabinets,  so  as  to  obviate  any  danger  of 
the  melted  fuse  metal  coming  in  contact  with  any  substance 
which  might  be  ignited  thereby. 

c.  Cut-outs    must   operate    successfully    on    short-circuits, 
under  the  most  severe  conditions  with  which  they  are  liable  to 


Single  Pole. 

Double  Pole. 
Figure  123 

meet  in  practice,  at  25  per  cent  above  their  rate  of  voltage  and 
the  fuses  rated  at  50  per  cent  above  the  current  for  which  the 
cut-out  is  designed. 

There  is  always  the  possibility  of  a  larger  fuse  being  put 
in  the  cut-out  than  it  was  designed  for.  Again,  the  voltage  in 
most  .plants  can,  under  some  conditions,  rise  considerably 
above  the  normal.  The  need  of  some  margin,  as  a  factor  of 
safety  to  prevent  the  cut-outs  from  being  ruined  in  ordinary 
service,  is  therefore  evident. 

The  most  severe  service  which  can  be  required  of  a  cut-out 
in  practice  is  to  open  a  "dead  short-circuit"  with  only  one 
fuse  blowing,  and  it  is  with  these  conditions  that  all  tests 
should  be  made.  (See  Section  j.) 


FITTINGS,  MATERIALS,  ETC. 


195 


d.  Circuit-breakers  must  operate  successfully  on  short-cir- 
cuits, under  the  most  severe  conditions  with  which  they  are 
liable  to  meet  in  practice,  when  set  at  50  per  cent  above  the 
current,  and  with  a  voltage  25  per  cent  above  that  for  which 
they  are  designed. 

For  the  same  reason  as  in  Section  c. 

e.  Must  be  plainly  marked  where  it  will  always  be  visible, 
with  the  name  of  the  maker,  and  current  and  voltage  for  which 
the  device  is  designed. 


Link-Fuse  Cut-Outs. 
(See  Figure  124.) 

The  following  rules  are  intended  to  cover  open  link  fuses 
mounted  on  slate  or  marble  bases,  including  switchboards, 
tablet-boards,  and  single  fuse-blocks.  They  do  not  apply  to 
fuses  mounted  on  porcelain  bases,  to  the  ordinary  porcelain 
cut-out  blocks,  enclosed  fuses,  or  any  special  or  covered  type 
of  fuse.  When  tablet-boards  or  single  fuse-blocks  with  such 
open  link  fuses  on  them  are  used  in  general  wiring,  they  must 
be  enclosed  in  cabinet  boxes  made  to  meet  the  requirements  of 
No.  54.  This  is  necessary,  because  a  severe  flash  may  occur 
when  such  fuses  melt,  so  that  they  would  be  dangerous  if 
exposed  in  the  neighborhood  of  any  combustible  material. 

f.  Base. — Must  be  mounted  on  slate  or  marble  bases. 
Bases  with  an  area  of  over  twenty-five  square  inches  must 


Figure  124 


Figure  125 


have  at  least  four  supporting  screws.  Holes  for  supporting 
screws  must  be  kept  outside  of  the  area  included  by  the  out- 
side edges  of  the  fuse-block  terminals,  and  must  be  so  located 
or  countersunk  that  there  will  be  at  least  one-half  an  inch 


1%  MODERN   ELECTRICAL   CONSTRUCTION. 

space,  measured  over  the  surface,  between  the  head  of  the 
screw  or  washer  and  the  nearest  live  part. 

g.  Mounting. — Nuts  or  screw-heads  on  the  under  side 
of  the  base  must  be  countersunk  not  less  than  one-eighth  inch, 
and  covered  with  a  waterproof  compound  which  will  not  melt 
below  150  degrees  Fahrenheit. 

h.  Metal. — All  fuse-block  terminals  must  have  ample  metal 
for  stiffness  and  to  prevent  rise  in  temperature  of  any  part  of 
over  50  degrees  Fahrenheit  at  full  load.  Terminals,  as  far  as 
practicable,  should  be  made  of  compact  form  instead  of  being 
rolled  out  in  thin  strips;  and  sharp  edges  or  thin  projecting 
pieces  as  on  winged  thumb  nuts  and  the  like  should  be  avoided. 
Thin  metal,  sharp  edges  and  projecting  pieces  are  much  more 
likely  to  cause  an  arc  to  start  than  a  more  solid  mass  of  metal. 
It  is  a  good  plan  to  round  all  corners  of  the  terminals  and  to 
chamfer  the  edges. 

i.  Connections. — Clamps  for  connecting  the  wires  to  the 
fuse-block  terminals  must  be  of  solid,  rugged  construction,  so 
as  to  insure  a  thoroughly  good  connection  and  to  withstand 
considerable  hard  usage.  For  fuses  rated  at  over  fifty  am- 
peres, lugs  firmly  screwed  or  bolted  to  the  terminals  and  into 
which  the  conducting  wires  are  soldered  must  be  used. 

See  not^  under  No.  51  h. 

j.  Test. — Must  operate  successfully  when  blowing  only 
one  fuse  at  a  time  on  short-circuits  with  fuses  rated  at  50 
per  cent  above  and  with  a  voltage  25  per  cent  above  the 
current  and  voltage  for  which  the  cut-out  is  designed. 

k.  Marking. — Must  be  plainly  marked,  where  it  will  be 
visible  when  the  cut-out  block  is  installed,  with  the  name  of 
the  maker  and  the  current  and  the  voltage  for  which  the 
block  is  designed. 

/.  Spacings. — Spacings  must  be  at  least  as  great  as  those 
given  in  the  following  table,  which  applies  only  to  plain,  open 
link-fuses  mounted  on  slate  or  marble  bases.  The  Spacings 
given  are  correct  for  fuse-blocks  to  be  used  on  direct-cur- 
rent systems,  and  can  therefore  be  safely  followed  in  devices 
designed  for  alternating  currents.  If  the  copper  fuse-tips  over- 


FITTINGS,   MATERIALS,  ETC.  197 

hang  the  edges  of  the  fuse-block  terminals,  the  spacings  should 
be  measured  between  the  nearest  edges  of  the  tips. 

125  volts  or  less: 

Minimum  Separation  of  Minimum 
Nearest  Metal  Parts  of  Break- 
Opposite  Polarity.  Distance. 

10   amperes   or  less %  inch.  %  inch. 

11-100  amperes    1         "  %     •« 

101-300         "            1         "  1         " 

301-1000       "          114     "  1%     " 

126  to  250  volts: 

10   amperes   or  less 1%  Inch.  1*4  inch. 

11-100  amperes  1%  "  1^  " 

101-300  "  .  .  2  "  l%  « 

301-1000  " 2%  "  2 

A  space  must  be  maintained  between  fuse  terminals  of  the 
same  polarity  of  at  least  one-half  inch  for  voltages  up  to  125 
and  of  at  least  three-quarter  inch  for  voltages  from  126  to  250. 
This  is  the  minimum  distance  allowable,  and  greater  separation 
should  be  provided  when  practicable. 

For  250  volt  boards  or  blocks  with  the  ordinary  front-con- 
nected terminals,  except  where  these  have  a  mass  of  compact 
form,  equivalent  to  the  back-connected  terminals  usually  found 
in  switchboard  work,  a  substantial  barrier  of  insulating  mate- 
rial, hot  less  than  one-eighth  of  an  inch  in  thickness,  must  be 
placed  in  the  "break  gap — this  barrier  to  extend  out  from  the 
base  at  least  one-eighth  of  an  inch  farther  than  any  bare  live 
part  of  the  fuse-block  terminal,  including  binding  screws,  nuts 
and  the  like.  (Figure  125.) 

For  three-wire  systems  cut-outs  must  have  the  break-dis- 
tance required  for  circuits  of  the  potential  of  the  outside  wires. 

Enclosed-Fuse   Cut-Outs,— Plug  and  Cartridge  Type. 
(See  Figure  126.) 

m.  Base. — Must  be  made  of  non-combustible,  non-ab- 
sorptive insulating  material.  Blocks  with  an  area  of  over 
twenty-five  square  inches  must  have  at  least  four  supporting 
screws.  Holes  for  supporting  screws  must  be  so  located  or 
countersunk  that  there  will  be  at  least  one-half  of  an  inch 
space,  measured  over  the  surface,  between  the  screw-head  or 
washer  and  the  nearest  live  metal  part,  and  in  all  cases  when 
between  parts  of  opposite  polarity  must  be  countersunk. 

«.  Mounting.— Nuts  or  screw-heads  on  the  under  side  of 
the  base  must  be  countersunk  at  least  one-eighth  of  an  inch 


198  MODERN   ELECTRICAL  CONSTRUCTION. 

and  covered  with  a  waterproof  compound  which  will  not  melt 
below  150  degrees  Fahrenheit. 

o.  Terminals. — Terminals  of  such  a  design  that  the  block 
cannot  be  easily  fused  with  anything  but  approved  enclosed 
fuses  are  recommended  for  blocks  of  all  capacities,  and  will 
be  required  on  blocks  having  a  rated  capacity  of  sixty  am- 


gure  126 


peres  or  less.  They  must  be  secured  to  the  base  by  two 
screws  or  the  equivalent,  so  as  to  prevent  them  from  turning, 
and  must  be  so  made  as  to  secure  a  thoroughly  good  contact 
with  the  fuse. 

p.  Connections. — Clamps  for  connecting  wires  to  the  ter- 
minals must  be  of  a  design  which  will  ensure  a  thoroughly 
good  connection,  and  must  be  sufficiently  strong  and  heavy  to 
withstand  considerable  hard  usage.  For  fuses  rated  to  carry 
over  sixty  amperes,  lugs  firmly  screwed  or  bolted  to  the  ter- 
minals and  into  which  the  connecting  wires  shall  be  soldered 
must  be  used. 

q.  Classification. — Must  be  classified  as  regards  both  cur- 
rent and  voltage,  and  must  be  so  designed  that  the  bases  of 
one  class  cannot  be  used  with  fuses  of  another  class  rated  for 
a  higher  current  or  voltage.  The  following  classification  is 
recommended : — 

0-250  Volts.  251-600  Volts. 
0-  30  amperes.  0-  30  amperes. 

31-  60          "  31-  60 

61-100          "  61-100 

101-200          "  101-200 

201-300          "  201-300 

301-500          "  301-500 

r.  Design. — Must  be  of  such  a  design  that  it  wil  not  be 
easy  to  form  accidental  short-circuits  across  live  metal  parts 
of  opposite  polarity  on  the  block  or  on  the  fuses  in  the  block. 

j.     Marking. — Must  be  marked,  where  it  will  be  plainly 


FITTINGS,   MATERIALS,  ETC.  199 

visible  when  the  block  is  installed,  with  the  name  of  the  maker 
and  the  voltage  and  range  of  current  for  which  it  is  designed. 

53.     Fuses. 

(For  installation  rules,  sec  Nos.  //  and  21.} 

Link  Fuses. 

a.  Terminals. — Must   have    contact    surfaces   or   tips    of 
harder   metal,   having  perfect  electrical  connections  with  the 
fusible  part  of  the  strip. 

The  use  of  the  hard  metal  tip  is  to  afford  a  strong  mechan- 
ical bearing  for  the  screws,  clamps,  or  other  devices  provided 
for  holding  the  fuse. 

b.  Rating. — Must  be  stamped  with  about  80  per  cent  of 
the  maximum  current  which  they  can  carry  indefinitely,  thus 
allowing  about  25  per  cent  overload  before  the  fuse  melts. 

With  naked  open  fuses,  of  ordinary  shapes  and  with  not 
over  500  amperes  capacity,  the  minimum  current  which  will 
melt  them  in  about  five  minutes  may  be  safely  taken  as  the 
melting  point,  as  the  fuse  practically  reaches  its  maximum 
temperature  in  this  time.  With  larger  fuses  a  longer  time  is 
necessary.  This  data  is  given  to  facilitate  testing. 

c.  Marking. — Fuse  terminals  must  be  stamped  with  the 
maker's  name  or  initials,  or  with  some  known  trade  mark. 


Enclosed  Fuses, — Plug  and  Cartridge  Type. 
(Sec  Figure  126.) 

d.  Construction. — The  fuse  plug  or  cartridge  must  be 
sufficiently  dust-tight  so  that  lint  and  dust  cannot  collect 
around  the  fusible  wire  and  become  ignited  when  the  fuse  is 
blown. 

The  fusible  wire  must  be  attached  to  the  plug  or  cartridge 
terminals  in  such  a  way  as  to  secure  a  thoroughly  good  con- 
nection and  to  make  it  difficult  for  it  to  be  replaced  when 
melted. 

c.  Classification. — Must  be  classified  to  correspond  with 
the  different  classes  of  cut-out  blocks,  and  must  be  so  designed 


200 


MODERN   ELECTRICAL  CONSTRUCTION. 


that  it  will  be  impossible  to  put  any  fuse  of  a  given  class  into 
a  cut-out  block  which  is  designed  for  a  current  or  voltage 
lower  than  that  of  the  class  to  which  the  fuse  belongs. 

f.  Terminals. — The    fuse    terminals    must   be    sufficiently 
heavy  to  ensure  mechanical  strength  and  rigidity. 

g.  Rating. — Must  be  rated  at  80  per  cent  of  the  maximum 
current  which  they  will  carry  indefinitely,  and  must  open  the 
circuit  within  five  minutes  when  a  current  50  per  cent  greater 
than  their  rated  capacity  is  passed  through  them. 

h.    Marking. — Must  be  marked,  where  it  will  be  plainly 


Three-Wire  Mains 
Figure  127 

visible,  with  the  name  or  trade  mark  of  the  maker  and  the 
voltage  and  current  for  which  the  fuse  is  designed. 

i.    Temperature   Rise. — The  temperature  of  the  exterior 
of  the  fuse  enclosure,  must  not  rise  more  than  125  degrees 


FITTINGS,   MATERIALS,  ETC.  201 

Fahrenheit  above  that  of  the  surrrounding  air  when  the  fuse 
is  carrying  the  current  for  which  it  is  rated. 

/.  Test. — Must  not  hold  an  arc  or  throw  out  melted  metal 
or  sufficient  flame  to  ignite  easily  inflammable  material  on  or 
near  the  cut-out,  when  only  one  fuse  is  blown  at  a  time  on  a 
short-circuit,  on  a  system  having  a  capacity  of  300  K.  W. 
or  over,  at  the  voltage  for  which  the  fuse  is  rated. 

A  number  of  fuses  having  considerable  merit  will  probably 
not  fully  stand  this  test.  Such  fuses  will  be  carefully  ex- 
amined and  tested,  and  approved  with  such  limitations  as 
safety  requires.  For  example,  a  fuse  which  might  be  quite 
satisfactory  in  the  small  sizes  or  with  a  moderate  amount  of 
resistance  in  circuit,  but  which  under  more  severe  conditions 
would  arc  considerably,  might  be  approved  without  reservation 
up  to  certain  limits  and  approved  beyond  these  limits  only 
when  enclosed  in  ctibinets  or  safely  removed  from  combustible 
materials.  Greater  deflniteness  appears  impossible  in  the 
present  state  of  the  art. 

53 A.    Tablet  and  Panel  Boards. 

(Sec  Figure  127. ~) 

The  following  minimum  distance  between  bare  live  metal 
parts  (bus-bars,  etc.)  must  be  maintained: — 

Between  parts  of  opposite  polarty  Between  parts  of 

except  at   switches  and  link  fuses.  same   polarity. 

When  mounted  on  When  held  free  At  link 

the  same  surface.  in  the  air.  fuses. 

0-125    volts      %  inch.  %  inch.  %  inch. 

126-250  volts   1»4      '  %      '  %      ' 

At  switches  or  enclosed  fuses,  parts  of  the  same  polarity 
may  be  placed  as  close  together  as  convenience  in  handling 
will  allow. 

It  should  be  noted  that  the  above  distances  are  the  mini- 
mum allowable,  and  it  is  urged  that  greater  distances  be 
adopted  wherever  the  conditions  will  permit. 

The  spacings  given  in  the  first  column  apply  to  the  branch 
conductors  where  enclosed  fuses  are  used.  Where  link  fuses 
or  knife  switches  are  used,  the  spacings  must  be  at  least  as 
great  as  those  required  by  Nos.  51  and  52. 

The  spacings  given  in  the  second  column  apply  to  the  dis- 
tance between  the  raised  main  bars,  and  between  these  bars  and 
the  branch  bars  over  which  they  pass. 

The  spacings  given  in  the  third  column  are  intended  to 
prevent  the  melting  of  a  link  fuse  by  the  blowing  of  an  ad- 
jacent fuse  of  the  same  polarity. 


MODERN   ELECTRICAL   CONSTRUCTION. 


54.    Cut-Out  Cabinets. 

a.  Material. — Cabinets  must  be  sub- 
stantially constructed  of  non-combusti- 
ble, non-absorptive  material,  or  of  wood. 
When  wood  is  use  dthe  inside  of  the  cabi- 
net must  be  completely  lined  with  a  non- 
combustible  insulating  material.  Slate  or 
marble  at  least  one-quarter  inch  in  thick- 
ness is  strongly  recommended  for  such 
lining,  but,  except  with  metal  conduit 
systems,  asbestos  board  at  least  one- 
eighth  inch  in  thickness  may  be  used  in 
dry  places  if  firmly  secured  by  shellac 
and  tacks. 

With  metal  conduit  systems  the  lining 
of  either  the  box  or  the  gutter  must  be 
one-sixteenth  inch  galvanized,  painted 
or  enameled  iron,  or  preferably  one- 
Fig.  128.  quarter  inch  slate  or  marble.  (Figure 
128.) 

The  object  of  the  lining  of  such  cut-out  cabinets  or  gutters 
is  to  render  the  same  approximately  fireproof  in  case  of  short 
circuit  after  the  wires  leave  the  protecting  metal  conduits. 

With  wood  cabinets  the  wood  should  be  thoroughly  filled 
and  painted  before  the  lining  is  put  in  place. 

b.  Door. — The  door  must  close  against  a  rabbet,  so  as  to 
be  perfectly  dust-tight.     Strong  hinges  and  a  strong  hook  or 
catch  are  required.     Glass  doors  must  be  glazed  with  heavy 
plate  glass,  not  less  than  three-sixteenths  of  an  inch  in  thick- 
ness, and  panes  should  not  exceed  one  foot  in  width.     A  space 
of  at  least  two  inches  must  be  allowed  between  the  fuses  and 
the  door.     This  is  necessary  to  prevent  cracking  or  breaking 
by  the  severe  blow  and  intense  heat  which  may  be  produced 
under  some  conditions. 

A  cabinet  Is  of  little  use  unless  the  door  is  kept  tightly 
closed,  and  especial  attention  is  therefore  called  to  the  impor- 
tance of  having  a  strong  and  reliable  catch  or  other  fastoning. 
A  spring  catch  is  advised  if  a  good  one  can  be  obtained,  but 
most  of  those  sold  for  use  on  cupboards,  etc.,  are  so  small 
that  they  fail  to  catch  when  the  door  shrinks  a  little,  or  are 
so  weak  that  they  soon  give  out. 

c.  Bushings. — Bushings  through  which  wires  enter  must 
fit  tightly  the  holes  in  the  box,  and  must  be  of  approved  con- 


FITTINGS,   MATERIALS,  ETC.  203 

struction.  The  wires  should  completely  fill  the  holes  in  the 
bushings,  using  tape  to  build  up  the  wire,  if  necessary,  so  as 
to  keep  out  the  dust. 

Rule  54  A.     New  Rule — Rosettes. 

(Sec  Figure  129.) 

Celling;  rosettes,  both'  fus*d  and  f useless,  must  be  con- 
structed in  accordance  with  the  following  specifications: 

a.  Base. — Current-carrying  parts  must  be  mounted  on  non- 
combustible,  non-absorptive  insulating  bases.  There  should  be 
no  openings  through  the  rosette  base  except  those  for  the 


Figure  129 

supporting  screws  and  in  the  concealed  type  for  the  con- 
ductors also,  and  these  openings  should  not  be  made  any 
larger  than  necessary. 

There  must  be  at  least  one-quarter  inch  space,  measured 
over  the  surface,  between  supporting  screws  and  current- 
carrying  parts.  The  supporting  screws  must  be  so  located 
or  countersunk  that  the  flexible  cord  cannot  come  in  con- 
tact with  them. 

Bases  for  the  knob  and  cleat  type  must  have  at  least  two 
holes  for  supporting  screws ;  must  be  high  enough  to  keep  the 
wires  and  terminals  at  least«one-half  inch  from  the  surface 
to  which  the  rosette  is  attached,  and  must  have  a  porcelain 
lug  under  each  terminal  to  prevent  the  rosette  from  being 
placed  over  projections  which  would  reduce  the  separation  to 
less  than  one-half  inch. 

Bases  for  the  moulding  and  conduit  box  types  must  be 
high  enough  to  keep  the  wires  and  terminals  at  least  three- 
eighths  inch  from  the  surface  wired  over. 


204  MODERN   ELECTRICAL  CONSTRUCTION. 

b.  Mounting. — Contact  pieces  and  terminals  must  be  se- 
cured in  position  by  at  least  two  screws,  or  made  with  a  square 
shoulder,  or  otherwise  arranged  to  prevent  turning. 

The  nuts  or  screw  heads  on  the  under  side  of  the  base  must 
be  countersunk  not  less  than  one-eighth  inch  and  covered  with 
a  waterproof  compound  which  will  not  melt  below  150  degrees 
Fahrenheit. 

c.  Terminals. — Line   terminal   plates   must    be    at    least 
.07  of  an   inch    in   thickness,   and   terminal   screws   must   not 
be  smaller  than  No.  6  standard  screw  with  about  32  threads 
per  inch. 

Terminal  plates  for  the  flexible  cord  and  for  fuses  must 
be  at  least  .06  of  an  inch  in  thickness,  and  the  terminal  screws 
must  not  be  smaller  than  No.  5  standard  screw  with  about  40 
threads  per  inch. 

d.  Cord  Inlet. — The  diameter  of  the  cord  inlet  hole  should 
measure  13/32"  in  order  that  standard  portable  cord  may  be 
used. 

e.  Knot   Space. — Ample   space   must  be  provided   for   a 
substantial  knot  tied  in  the  cord  as  a  whole. 

All  parts  of  the  rosette  upon  which  the  knot  is  likely  to 
bear  must  be  smooth  and  well  rounded. 

f.  Cover. — When  the   rosette  is   made  in  two  parts,  the 
cover  must  be  secured  to  the  base  so  that  it  will  not  work 
loose. 

In  fused  rosettes,  the  cover  must  fit  closely  over  the  base 
so  as  to  prevent  the  accumulation  of  dust  or  dirt  on  the  inside, 
and  also  to  prevent  any  flash  or  melted  metal  from  being 
thrown  out  when  the  fuses  melt. 

g.  Markings. — Must  be  plainly  marked  where  it  may  read- 
ily be  seen  after  the  rosette  has  been  installed,  with  the  name  or 
trade  mark  of  the  manufacturer,  and  the  rating  in  amperes 
and  volts.     Fuseless  rosettes  may  be  rated  3  amperes,  250  volts ; 
fused  rosettes,  with  link  fuses,  not  over  2  amperes,  125  volts. 

g.  Test. — Fused  rosettes  must  have  a  fuse  in  each  pole 
and  must  operate  successfully  when  short-circuited  on  the  vol- 
tage for  which  they  are  designed,  the  test  being  made  with 
the  two  fuses  in  circuit. 

NOTE. — When  link  fuses  are  used  the  test  shall  be  made  with 
fuse  wire  which  melts  at  ahout  7  amperes  in  one  inch  lengths. 
The  larger  fuse  is  specified  for  the  test  in  order  to  more  nearly 


FITTINGS,   MATERIALS,  ETC.  205 

approximate    the    severe    conditions    obtained    when    only    one 
2-ampere  fuse  (the  rating  of  the  rosette)  is  blown  at  a  time. 

Fused    rosettes    equipped    with    enclosed    fuses    are    much 
preferable  to  the  link  fuse  rosettes. 

55.     Sockets. 

(See  Figure  130.) 

(For  installation  rules,  see  No.  27.) 

Sockets   of  all  kinds,    including  wall   receptacles,   must  be 
constructed  in  accordance  with  the  following  specifications: 

a.  Standard  Sizes. — The  standard  lamp  socket  must  be 
suitable  for  use  on  any  voltage  not  exceeding  250  and  with 
any  size  lamp  up  to  fifty  candle-power.     For  lamps  larger  than 
fifty  candle-power  a  standard  keyless  socket  may  be  used,  or 
if  a  key  is  required,  a  special  socket  designed  for  the  current 
to  be  used  must  be  made.     Any  special  sockets  must  follow  the 
general  spirit  of  these  specifications. 

b.  Marking. — The  standard  socket  must  be  plainly  marked 
250v.,  50  c.  p.,  and   with  the  manufacturer's  name  or  regis- 
tered trade  mark.     Special  sockets  must  be  marked  with  the 
current  and  voltage  for  which  they  are  designed. 

r.     Shell. — Metal  used  for  shells  must  be  moderately  hard, 
but  not  hard  enough  to  be  brittle  or  so  soft  as  to  be  easily 


Figure  130 


dented  or  knocked  out  of  shape.  Brass  shells  must  be  at  least 
thirteen  one-thousandths  of  an  inch  in  thickness,  and  shells 
of  any  other  material  must  be  thick  enough  to  give  the  same 
stiffness  and  strength  as  the  required  thickness  of  brass. 

d.  Lining. — The  inside  of  the  shells  must  be  lined  with 
insulating  material,  which  must  absolutely  prevent  the  shell 
from  becoming  a  part  of  the  circuit,  even  though  the  wires 
inside  the  socket  should  start  from  their  position  under  the 
binding  screws. 


206  MODERN   ELECTRICAL  CONSTRUCTION. 

The  material  used  for  lining  must  be  at  least  one  thirty- 
second  of  an  inch  in  thickness,  and  must  be  tough  and  tena- 
cious. It  must  not  be  injuriously  affected  by  the  heat  from  the 
largest  lamp  permitted  in  the  socket,  and  must  leave  water 
in  which  it  is  boiled  practically  neutral.  It  must  be  so  firmly 
secured  to  the  shell  that  it  will  not  fall  out  with  ordinary 
handling  of  the  socket.  It  is  preferable  to  have  the  lining  in 
one  piece. 

The  cap  must  also  be  lined,  and  this  lining  must  comply 
with  the  requirements  for  shell  linings. 

The  shell  lining  should  extend  beyond  the  shell  far  enough 
so  that  no  part  of  the  lamp  base  is  exposed  when  a  lamp  is  in 
the  socket. 

e.  Cap. — Caps,  when  of  sheet  brass,  must  be  at  least  thir- 
teen one-thousandths  of  an  inch  in  thickness,  and  when  cast 
or  made  of  other  metals  must  be  of  equivalent  strength.  The 
inlet  piece,  except  for  special  sockets,  must  be  tapped  with 
a  standard  one-eighth-inch  pipe  thread.  It  must  contain 
sufficient  metal  for  a  full,  strong  thread,  and  when  not  in  one 
piece  with  the  cap,  must  be  joined  to  it  in  such  a  way  as  to 
give  the  strength  of  a  single  piece. 

There  must  be  sufficient  room  in  the  cap  to  enable  the 
ordinary  wireman  to  easily  and  quickly  make  a  knot  in  the 
cord  and  to  push  it  into  place  in  the  cap  without  crowding. 
All  parts  of  the  cap  upon  which  the  knot  is  likely  to  bear  must 
be  smooth  and  well  insulated. 

The  cap  lining  called  for  In  the  note  to  Section  d  will  pro- 
vide a  sufficiently  smooth  and  well-insulated  surface  for  the 
knot  to  bear  upon. 

Sockets  with  an  outlet  threaded  for  three-eighths  inch 
pipe  will,  of  course,  be  approved  where  circumstances  demand 
their  use.  This  size  outlet  is  necessary  with  most  stiff 
pendants  and  for  the  proper  use  of  reinforced  flexible  cord,  as 
explained  in  the  note  to  No.  28  </. 

/.  Frame  and  Screws. — The  frame  which  holds  the  mov- 
ing parts  must  be  sufficiently  heavy  to  give  ample  strength  and 
stiffness. 

Brass  pieces  containing  screw  threads  must  be  at  least 
six  one-hundredths  of  an  inch  in  thickness. 

Binding  post  screws  must  not  be  smaller  than  No.  5  stand- 
ard screw  with  about  40  threads  per  inch. 

g.     Spacing. — Points   of  opposite   polarity  must  every- 


FITTINGS,   MATERIALS,  ETC.  207 

where  be  kept  not  less  than  three  sfxty-fourths  of  an  inch 
apart,  unless  separated  by  a  reliable  insulation. 

//.  Connections. — The  connecting  points  for  the  flexible 
cord  must  be  made  to  very  securely  grip  a  No.  16  or  18  B. 
&  S.  gage  conductor.  A  turned-up  lug,  arranged  so  that  the 
cord  may  be  gripped  between  the  screw  and  the  lug  in  such 
a  way  that  it  cannot  possibly  come  out,  is  strongly  advised. 

i.  Lamp  Holder. — The  socket  must  firmly  hold  the  lamp 
in  place  so  that  it  cannot  be  easily  jarred  out,  and  must  pro- 
vide a  contact  good  enough  to  prevent  undue  heating  with  the 
maximum  current  allowed.  The  holding  pieces,  springs,  and 
the  like,  if  a  part  of  the  circuit,  must  not  be  sufficiently  ex- 
posed to  allow  them  to  be  brought  in  contact  with  anything 
outside  of  the  lamp  and  socket. 

j.  Base. — With  the  exception  of  the  lining  all  parts  of 
insulating  material  inside  the  shell  must  be  made  of  por- 
celain. 

k.  Key. — The  socket  key-handle  must  be  of  such  a  ma- 
terial that  it  will  not  soften  fnm  the  heat  of  a  fifty  candle- 
power  lamp  hanging  downwards  from  the  socket  in  air  at  70 
degrees  Fahrenheit,  and  must  be  securely,  but  not  necessarily 
rigidly,  attached  to  the  metal  spindle  which  it  is  designed  to 
turn. 

/.  Sealing. — All  screws  in  porcelain  pieces,  which  can  be 
firmly  sealed  in  place,  must  be  so  sealed  by  a  waterproof  com- 
pound which  will  not  melt  below  200  degrees  Fahrenheit. 

m.  Putting  Together. — The  socket  as  a  whole  must  be  so 
put  together  that  it  will  not  rattle  to  pieces.  Bayonet  joints  or 
an  equivalent  are  recommended. 

H.  Test. — The  socket,  when  slowly  turned  "on  and  off" 
at  the  rate  of  about  two  or  three  times  per  minute,  while 
carrying  a  load  of  one  ampere  at  250  volts,  must  "make  and 
break"  the  circuit  6,000  times  before  failing. 

o.  Keyless  Sockets.— Keyless  sockets  of  all  kinds  must 
comply  with  the  requirements  for  key  sockets  as  far  as  they 
apply. 

/>.  Sockets  of  Insulating  Material. — Sockets  made  of 
porcelain  or  other  insulating  material  must  conform  to  the 


208  MODERN   ELECTRICAL  CONSTRUCTION. 

above  requirements  as  far  as  they  apply,  and  all  parts  must 
be  strong  enough  to  withstand  a  moderate  amount  of  hard 
usage  without  breaking. 

Porcelain  shell  sockets  being  subject  to  breakage,  and 
constituting  a  hazard  when  broken,  will  not  be  accepted  for 
use  in  places  where  they  would  be  exposed  to  hard  usage. 

q.  Inlet  Bushing. — When  the  socket  is  not  attached 
to  a  fixture,  the  threaded  inlet  must  be  provided  with  a  strong 
insulating  bushing  having  a  smooth  hole  at  least  nine  thirty- 
seconds  of  an  inch  in  diameter.  The  edges  of  the  bushing 
must  be  rounded  and  all  inside  fins  removed,  so  that  in  no  place 
will  the  cord  be  subjected  to  the  cutting  or  wearing  action  of 
a  sharp  edge. 

Bushings  for  sockets  having  an  outlet  threaded  for  three- 
eights-inch  pipe  should  have  a  hole  thirteen  thirty-seconds  of 
an  inch  in  diameter,  so  that  they  will  accommodate  approved 
reinforced  flexible  cord. 


56.     Hanger-Boards. 

(See  Figure  131.) 

a.  Hanger-boards  must  be  so  constructed  that  all  wires 
and  current-carrying  devices  thereon  will  be  exposed  to  view 
and  thoroughly  insulated  by  being  mounted  on  a  non-com- 


Figure  131 

bustible,  non-absorptive  insulating  substance.  All  switches 
attached  to  the  same  must  be  so  constructed  that  they  shall 
be  automatic  in  their  action,  cutting  off  both  poles  to  the  lamp, 
not  stopping  between  points  when  started  and  preventing  an 
arc  between  points  under  all  circumstances. 


FITTINGS,   MATERIALS,  ETC. 


209 


57.    Arc  Lamps. 

(See   Figure   132.) 

(For  installation  rules,  see  Nos.  19  and  29.) 

a.  Must  be  provided   with   reliable  stops  to  prevent  car- 
bons from  falling  out  in  case  the  clamps  become  loose. 

b.  All  exposed  parts  must  be  carefully  insulated  from  the 


c.     Must,   for  constant-current  systems,  be  provided  with 
an  approved  hand  switch,  and  an  automatic  switch  that  will 
shunt  the  current  around  the  carbons, 
should  they  fail  to  feed  properly. 

The  hand  switch  to  be  approved,  if 
placed  anywhere  except  on  the  lamp 
itself,  must  comply  with  requirements 
for  switches  on  hangerboards  as  laid 
down  in  No.  56. 

58.    Spark  Arresters. 

(Sec  Figure  132.} 

(For  installation  rules,  sec  Nos.  19  c 
and  29  c.) 

a.  Spark  arresters  must  so  close 
the  upper  orifice  of  the  globe  that  it 
will  be  impossible  for  any  sparks, 
thrown  out  by  the  carbons,  to  escape. 


Fig.  132. 


59.     Insulating  Joints. 

(See  No.  26  a.) 

a.  Must  be  entirely  made  of  material  that  will  resist  the 
action  of  illuminating  gases,  and  will  not  give  way  or  soften 
under  the  heat  of  an  ordinary  gas  flame  or  leak  under  a  mod- 
erate pressure.  Must  be  so  arranged  that  a  deposit  of  moisture 
will  not  destroy  the  insulating  effect ;  must  show  a  dielectric 
strength  between  gas-pipe  attachments  sufficient  to  resist 
throughout  five  minutes  the  application  of  an  electro-motive 
force  of  4,000  volts;  and  must  be  sufficiently  strong  to  resist 
the  strain  to  which  they  are  liable  to  be  subjected  during  instal- 
lation. 


210  MODERN   ELECTRICAL  CONSTRUCTION. 

b.  Insulating  joints  having  soft  rubber  in  their  construc- 
tion will  not  be  approved. 

60.    Rheostats. 

(For  installation  rules,  see  Nos.  4  a  and  8  c.) 

a.  Materials. — Must  be  made  entirely  of  non-combustible 
materials  except  such  minor  parts  as  handles,  magnet  insula- 
tion, etc. 

All  segments,  lever  arms,  etc.,  must  be  mounted  on  non- 
combustible,  non-absorptive,  insulating  material. 

Resistance  boxes  are  used  for  the  express  purpose  of  op- 
posing the  passage  of  current,  and  are  therefore  very  liable  to 
get  exceedingly  hot.  Hence  they  should  have  no  combustible 
material  in  their  construction. 

b.  Construction. — Must   have   legs   which   will   keep   the 
current-carrying  parts  at  least  one  inch  from  the  surface  on 
which  the  rheostat  is  mounted. 

The  construction  throughout  must  be  heavy,  rugged,  and 
thoroughly  workmanlike. 

c.  Connections. — Clamps    for    connecting    wires    to    the 
terminals  must  be  of  a  design  which  will  ensure  a  thoroughly 
good  connection,  and  must  be  sufficiently  strong  and  heavy  to 
withstand  considerable  hard  usage.     For  currents  above  fifty 
amperes,  lugs  firmly  screwed  or  bolted  to  the  terminals,  and 
into  which  the  connecting  wires   shall   be   soldered,  must  be 
used. 

Clamps  or  lugs  will  not  be  required  when  leads  designed 
for  soldered  connections  are  provided. 

d.  Marking. — Must  be  plainly  marked,  where  it  may  be 
readily  seen  after  the  device  is  installed,  with  the  rating  and 
the  name  of  the  maker;  and  the  terminals  of  motor-starting 
rheostats  must  be  marked  to  indicate  to  what  part  of  the  circuit 
each  is  to  be  connected,  as  "line,"  "armature,"  and  "field." 

c.  Contacts. — The  design  of  the  fixed  and  movable  con- 
tacts and  the  resistance  in  each  section  must  be  such  as  to 
secure  the  least  tendency  toward  arcing  and  roughening  of  the 
contacts,  even  with  careless  handling  or  the  presence  of  dirt. 

In  motor-starting  rheostats,  the  contact  at  which  the  cir- 
cuit is  broken  by  the  lever  arm  when  moving  from  the  running 


FITTINGS,    MATERIALS,  ETC.  211 

to  the  starting  position,  must  be  so  designed  that  there  will 
be  no  detrimental  arcing.  The  final  contact,  if  any,  on  which 
the  arm  is  brought  to  rest  in  the  starting  position  must  have 
no  electrical  connection. 


ui   on    tne  arc,  F. 
tend  to  spread  it  out  and  thus  dissipate  it 


f.  No-voltage    release. — Motor-starting    rheostats    must 
be  so  designed  that  the  contact  arm  cannot  be  left  on  interme- 
diate segments,  and  must  be  provided  with  an  automatic  device 
which  will  interrupt  the  supply  circuit  before  the  speed  of  the 
motor  falls  to  less  than  one-third  of  its  normal  value. 

g.  Overload-release. — Overload-release  devices  which  are 
inoperative  during  the  process  of  starting  a  motor  will  not  be 
approved,  unless  other  circuit-breakers  or  fuses  are  installed 
in  connection  with  them. 

If,  for  instance,  the  overload-release  device  simply  releases 
the  starting  arm  and  allows  it  to  fly  hack  and  break  the  circuit, 
it  is  inoperative  while  the  arm  is  being  moved  from  the  start- 
ing to  the  running  position. 

h.  Test.— Must,  after  100  operations  under  the  most 
severe  normal  conditions  for  which  the  device  is  designed, 
show  no  serious  burning  of  the  contacts  or  other  faults,  and 
the  release  mechanism  of  motor-starting  rheostats  must  not  be 
impaired  by  such  a  test. 

Field  rheostats,  or  main-line  regulators  intended  for  con- 
tinuous use,  must  not  be  burned  out  or  depreciated  by  carrying 
the  full  normal  current  on  any  step  for  an  indefinite  period. 
Regulators  intended  for  intermittent  use  (such  as  on  electric 
cranes,  elevators,  etc.)  must  be  able  to  carry  their  rated  cur- 
rent on  any  step  for  as  long  a  time  as  the  character  of  the 
apparatus  which  they  control  will  permit  them  to  be  used 
continuously. 

61.    Reactive  Coils  and  Condensers. 

a.  Reactive    coils     must     he     made     of     non-combustible 
material,  mounted  on  non-combustible  bases  and  treated,  in 
general,  as  sources  of  heat. 

b.  Condensers  must  be  treated  like  other  apparatus  oper- 
ating with  equivalent  voltage  and  currents.     They  must  have 


212  MODERN   ELECTRICAL  CONSTRUCTION. 

non-combustible  cases  and  supports,  and  must  be  isolated  from 
all  combustible  materials  and,  in  general,  treated  as  sources 
of  heat. 

62.  Transformers. 

{For  installation  rules,  see  Nos.  n,  is,  13  A  and  36.) 

a.  Must  not  be  placed  in  any  but  metallic  or  other  non- 
combustible  cases. 

On  account  of  the  possible  dangers  from  burn-outs  In  the 
coils.  (See  note  under  No.  11  a.) 

It  is  advised  that  every  transformer  be  so  designed  and 
connected  that  the  middle  point  of  the  secondary  coil  can 
be  reached  if,  at  any  future  time,  it  should  be  desired  to 
ground  it. 

b.  Must  be  constructed  to  comply  with  the  following  tests : 

1.  Shall  be  run  for  eight  consecutive  hours  at  full  load 

in  watts  under  conditions  of  service,  and  at  the 
end  of  that  time  the  rise  in  temperature,  as  meas- 
ured by  the  increase  of  resistance  of  the  primary 
coil,  shall  not  exceed  135  degrees  Fahrenheit. 

2.  The    insulation   of   transformers   when   heated    shall 

withstand  continuously  for  five  minutes  a  differ- 
ence of  potential  of  10,000  volts  (alternating)  be- 
tween the  primary  and  secondary  coils  and  be- 
tween the  primary  coils  and  core,  and  a  no-load 
"run"  at  double  voltage  for  thirty  minutes. 

63.  Lightning  Arresters. 

(For  installation  rules,  see  No.  5.) 

a.  Must  be  mounted  on  non-combustible  bases ;  must  be  so 
constructed  as  not  to  maintain  an  arc  after  the  discharge  has 
passed ;  must  have  no  moving  parts. 


CLASS  E. 

MISCELLANEOUS. 
64.    Signaling  Systems. 

Governing  wiring  forvtelephone,  telegraph,  district  mes- 
senger and  call-bell  circuits,  fire  and  burglar  alarms,  and 
all  similar  systems. 

a.  Outside  wires  should  be  run  in  underground  ducts  or 
strung  on  poles,  and,  as  far  as  possible,  kept  off  of  buildings, 
and  must  not  be  placed  on  the  same  cross-arm  with  electric 
light  or  power  wires.     They  should  not  occupy  the  same  duct, 
manhole  or  handhole  of  conduit  systems  with  electric  light  or 
power  wires. 

Single  manholes,  or  handholes,  may  be  separated  into  sec- 
tions by  means  of  partitions  of  brick  or  tile  so  as  to  be  con- 
sidered as  conforming  with  the  above  rule. 

b.  When  outside  wires  are  run  on  same  pole  with  electric 
light  or  power  wires,  the  distance  between  the  two  inside  pins 
of  each  cross-arm  must  not  be  less  than  twenty-six  inches. 

c.  All    aerial     conductors    and     underground     conductors 
which  are  directly  connected  to  aerial  wires  must  be  provided 
with  some  approved  protective  device,  which  must  be  located 
as  near  as  possible  to  the  point  where  they  enter  the  building, 
and  not  less  than  six  inches  from  curtains  or  other  inflammable 
material. 

d.  If  the  protector  is  placed  inside  of  building,  wires  from 
outside    support   to   binding-posts   of   protector,   must   comply 
with  the  following  requirements: 

1.  Must  be  of  copper,  and  not  smaller  than  No.  18  B.  & 

S.  gage. 

2.  Must   have   an   approved   rubber   insulating  covering 

(see  No.  41). 

3.  Must  have  drip  loops  in  each  wire  immediately  out- 

side the  building. 

4.  Must  enter  buildings  through  separate  holes  sloping 

upward  from  the  outside;  when  practicable,  holes 
to  be  bushed  with  non-absorptive,  non-combustible 
insulating  tubes  extending  through  their  entire 
length.  Where  tubing  is  not  practicable  the  wires 
shall  be  wrapped  with  two  layers  of  insulating 
tape. 


214  MODERN   ELECTRICAL  CONSTRUCTION. 

5.  Must  be  supported  on  porcelain   insulators,   so  that 

they  will  not  come  in  contact  with  anything  other 
than  their  designed  supports. 

6.  A  separation  between  wires  of  at  least  two  and  one- 

half  inches  must  be  maintained. 

In  case  of  crosses  these  wires  may  become  a  part  of  a 
high-voltage  circuit,  so  that  care  similar  to  that  given  high- 
voltage  circuits  is  needed  in  placing  them.  Porcelain  bushings 
at  the  entrance  holes  are  desirable,  and  this  requirement  is 
f  nly  waived  under  adverse  conditions,  because  the  state  of 
t  e  art  in  this  type  of  wiring  makes  an  absolute  requirement 
inadvisable. 

c.  The  ground  wire  of  the  protective  device  shall  be  run  in 
accordance  with  the  following  requirements : 

1.  Shall  be  of  copper,  and  not  smaller  than  No.  18  B.  & 

S.  gage. 

2.  Must   have   an   approved   rubber   insulating  covering 

(see  No.  41). 

3.  Must  run  in  as  straight  a  line  as  possible  to  a  good, 

permanent  ground,  to  be  made  by  connecting  to 
water  or  gas  pipe,  preferably  water  pipe.  If  gas 
pipe  is  used,  the  connection,  in  all  cases,  must  be 
made  between  the  meter  and  service  pipes.  In 
the  absence  of  other  good  ground,  connection  must 
made  to  a  metallic  plate  or  bunch  of  wires  buried 
in  permanently  moist  earth. 

In  attaching  a  ground  wire  to  a  pipe  it  is  often  difficult 
to  make  a  thoroughly  reliable  solder  joint.  It  is  better,  there- 
fore, where  possible,  to  carefully  solder  the  wire  to  a  brass 
plug,  which  may  then  be  firmly  screwed  into  a  pipe  fitting. 

Where  such  joints  are  made  under  ground  they  should  be 
thoroughly  painted  and  taped  to  prevent  corrosion. 

f.  The  protector  to  be  approved  must  comply  with  the  fol- 
lowing requirements : 

1.  Must  be  mounted  on  non-combustible,  non-absorptive 

insulating  bases,  so  designed  that  when  the  pro- 
tector is  in  place,  all  parts  which  may  be  alive  will 
be  thoroughly  insulated  from  the  wall  to  which 
the  protector  is  attached. 

2.  Must  have  the  following  parts  : 

A  lightning  arrester  which  will  operate  with  a  differ- 
ence of  potential  between  wires  of  not  over  500 
volts,  and  so  arranged  that  the  chance  of  acci- 
dental grounding  is  reduced  to  a  minimum. 


MISCELLANEOUS.  215 

A  fuse  designed  to  open  the  circuit  in  case  the  wires 
become  crossed  with  light  or  power  circuits:  The 
fuse  must  be  able  to  open  the  circuit  without  arc- 
ing or  serious  flashing  when  crossed  with  any 
ordinary  commercial  light  or  power  circuit. 
A  heat  coil,  if  the  sensitiveness  of  the  instrument  de- 
mands it,  which  will  operate  before  a  sneak  cur- 
rent can  damage  the  instrument  the  protector  is 
guarding. 

Heat  coils  are  necessary  In  all  circuits  normally  closed 
through  magnet  windings,  which  cannot  indefinitely  carry  a 
current  of  at  least  five  amperes. 

The  heat  coil  is  designed  to  warm  up  and  melt  out  with 
a  current  large  enough  to  endanger  the  instruments  if  con- 
tinued for  a  long  time,  hut  so  small  that  it  would  not  blow 
the  fuses  ordinarily  found  necessary  for  such  instruments. 
These  smaller  currents  are  often  called  "sneak"  currents. 

3.  The  fuses  must  be  so  placed  as  to  protect  the  arrester 
and  heat  coils,  and  the  protector  terminals  must 
be  plainly  marked  "line,"  "instruments,"  "ground." 

g.  Wires  beyond  the  protector,  except  where  bunched, 
must  be  neatly  arranged  and  securely  fastened  in  place  in  some 
convenient,  workmanlike  manner.  They  must  not  come  nearer 
than  six  inches  to  any  electric  light  or  power  wire  in  the 
building  unless  encased  in  approved  tubing  so  secured  as  to 
prevent  its  slipping  out  of  place. 

The  wires  would  ordinarily  be  insulated,  but  the  kind  of 
insulation  is  not  specified,  ns  the  protector  is  relied  upon  to 
stop  all  dangerous  currents.  Porcelain  tubing  or  approved 
flexible  tubing  may  be  .used  for  encasing  wires  where  re- 
quired as  above. 

h.  Wires  connected  with  outside  circuits,  where  bunched 
together  within  any  building,  rr  inside  wires,  where  laid  in 
conduits  or  ducts  with  electric  light  or  power  wires,  must  have 
fire-resisting  coverings,  or  else  must  be  enclosed  in  an  air- 
tight tube  or  duct. 

It  is  feared  that  if  a  burnable  insulation  were  used,  a 
chance  spark  might  ignite  it  and  cause  a  serious  fire,  for 
many  insulations  contain  a  large  amount  of  very  readily 
burnable  matter. 

65.    Electric  Gas  Lighting. 

a.  Electric  gas  lighting  must  not  be  used  or  the  same  fix- 
ture with  the  electric  light. 


216 


MODERN   ELECTRICAL   CONSTRUCTION. 


65A.    Moving  Picture  Machines. 

a.  Top  reel  must  be  encased  in  an  iron  box  with  hole  at 
the  bottom  only  large  enough  for  film  to  pass  through,  and 
cover  so  arranged  that  this  hole  can  be  instantly  closed.     No 
solder  to  be  used  in  the  construction  of  this  box. 

b.  A  box  must  be  used  for  receiving  the  film  after  being 
shown,  made  of  galvanized  iron  with  a  hole  in  the  top  only 
large  enough  for  the  film  to  pass  through  freely,  with  a  cover 
so  arranged  that  this  hole  can  be  instantly  closed.     An  opening 
may  be  placed  at  the  side  of  the  box  to  take  the  film  out,  with 
a  door  hung  at  the  top,  so  arranged  that  it  cannot  be  entirely 
opened,  and  provided  with  a  spring  catch  to  lock  it  closed. 
No  solder  to  be  used  in  the  construction  of  this  box. 

c.  The  handle  or  crank  used  in  operating  the  machine  must 
be  secured  to  the  spindle  or  shaft  so  that  there  will  be  no  lia- 
bility of  its  coming  off  and  allowing  the  film  to  stop  in  front 
of  the  lamp. 

d.  A  shutter  must  be  placed  in   front  of  the  condenser, 
arranged  so  as  to  be  normally  closed,  and  held  open  by  pres- 
sure of  the  foot. 

e.  A  metal  pan  must  be  placed  under  the  arc  lamp  to  catch 
all  sparks. 

f.  Extra  films  must  be  kept  in  metal  box  with  tight-fitting 
covers. 


66.    Insulation  Resistance. 

The  wiring  in  any  building  must  test  free  from  grounds; 
i.  e.,  the  complete  installation  must  have  an  insulation  between 
conductors  and  between  all  conductors  and  the  ground  (not 
including  attachments,  sockets,  receptacles,  etc.)  not  less  than 
that  given  in  the  following  table : 


Up  to 


5  amperes. 
10 


25 
50 
100 
200 
400 
800 
1,600 

The  test  must  be  made  with  all  cut-outs  and  safety  de- 
vices in  place.  If  the  lamp  sockets,  receptacles,  electroliers, 
etc.),  are  also  connected,  only  one-half  of  the  resistance  speci- 
fied in  the  table  will  be  required. 


.  .4,000,000  ohms 
.2,000,000 
.  800,000 
.  400,000 
.  200,000 
.  100,000 

50,000 

25,000 

12,500 


PRACTICAL   HINTS.  21? 

PRACTICAL  HINTS. 

A  full  description  of  the  Wheatstone  bridge,  the  telephone, 
magneto  and  ether  instruments,  as  well  as  the  many  ways  of 
their  application  in  testing  for  defects  and  for  circuits  in  elec- 
trical installations  having  been  given  in  a  previous  work  of  the 
authors  (Wiring  Diagrams  and  Descriptions}  it  is  not  thought 
necessary  to  repeat  them  here,  especially  as  a  work  of  this 
kind  is  necessarily  limited  in  diagrams  which  would  be  re- 
quired to  a  full  understanding  of  methods-.  This  chapter  will, 
therefore,  consist  only  of  such  hints  and  instructions  as  apply 
to  general  work. 

An  electric  light  circuit  may  be  tested  for  "short  circuit"  by 
connecting  an  incandescent  lamp  in  place  of  one  of  the  fuses. 
If  the  lamp  burns  while  there  are  no  lamps  in  circuit,  there  is 
sure  to  be  a  short  circuit.  A  low  candle-power  lamp  will  indi- 
cate with  less  current  than  a  high-candle-power  lamp  and  is, 
therefore,  better.  If  no  lamp  is  available  a  small  fuse  should 
first  be  tried. 

A  test  for  "ground"  may  be  made  in  the  same  way,  but  the 
lamp  must  be  connected  to  both  sides  in  turn  and  the  fuse  left 


»O/« 

in* 

000000000000 

Figure  133 

out.  If  the  main  system  to  which  the  circuit  to  be  tested  con- 
nects is  not  grounded,  a  temporary  ground  must  be  put  on. 
This  is  best  done  by  connecting  a  lamp  with  one  wire  to  a  gas 
or  water  pipe  and  the  other  to  the  "live"  binding  screw  on  the 
opposite  side  of  cutout  to  that  in  which  the  other  lamp  is  con- 
nected. Thus,  in  Figure  133,  if  a  ground  should  exist  at  3  and 
the  lamp  be  connected  to  gas  pipe,  as  shown,  the  test  lamp  at  1 
would  burn. 


218  MODERN   ELECTRICAL   CONSTRUCTION. 

If  a  voltmeter  were  connected  in  place  of  either  of  the 
lamps,  the  test  would  be  much  more  searching. 

With  3-wire  systems  no  ground  need  be  put  on,  as  the  neu- 
tral wire  will  always  be  found  grounded.  The  lamp  need  be 
tried  in  the  outside  fuses  only.  This  test  will  be  more  search- 
ing if  lamps  are  placed  in  all  sockets  connected. 

In  placing  fuses  in  the '3-wire,  110-220  volt  system,  the  neu- 
tral wire  should  always  be  fused  first. 

By  reference  to  Figure  134  it  will  be  seen  that  while  the 
neutral  fuse  in  main' blocks  a  is  out,  the  two  circuits  of  lamps 
c  and  d  must  burn  in  series;  that  is,  just  as  much  current  must 
pass  through  one  circuit  as  through  the  other.  So  long  as 
there  is  an  equal  number  of  lamps  in  each  circuit  there  is  no 
trouble;  but  should  most  of  the  lamps  in  one  circuit  be  turned 
off,  those  remaining  would  have  to  carry  all  the  current  that 
passes  through  the  lamps  of  the  other  circuit.  This  current 
would  overheat  them  and  break,  or  burn  them  out  in  a  very 
short  time.  If  the  neutral  fuse  is  in  place,  each  circuit  is  inde- 
pendent of  the  other  and  the  neutral  wire  only  carries  the 
difference  in  current  between  the  two  sets  of  lamps.  In  order 
to  insure  against  a  neutral  fuse  "blowing"  first  in  case  of 
trouble,  it  is  generally  made  heavier  than  in  the  outside  wires. 
When  a  3-wire  circuit  is  to  be  cut  off,  the  outside  fuses  should 
be  drawn  first. 

In  order  to  find  which  is  the  "neutral"  wire,  two  110  volt 
lamps  are  connected  in  series  and  the  wires  from  them  brought 
in  contact  with  two  of  the  three  wires.  If  both  lamps  burn  at 
full  candle  power  we  have  220  volts,  which  is  the  pressure  of  the 
outside  wires,  and,  therefore,  the  other  wire  must  be  the  neu- 
tral. If  the  lamps  burn  only  at  half  candle  power,  we  have 
only  110  volts  and  one  of  the  wires  must  be  the  neutral.  That 
wire  which  gives  110  volts  with  either  one  of  the  other  two 
wires  is  the  neutral;  this  wire  should  always  be  run  in  the 
center  between  the  other  two. 


PRACTICAL   HINTS. 


219 


A  test  for  the  neutral  wire  can  also  be  made  by  connecting 
a  lamp  to  ground.  A  lamp  connected  this  way  will  burn  from 
either  of  the  outside  wires,  but  not  from  the  neutral. 

If  the  neutral  wire  should  be  connected  to  any  but  the 
middle  binding  post  of  3-wire  cutouts  and  the  outside  wire 
to  the  other  two,  one-half  of  the  lamps  would  be  almost  imme- 
diately destroyed,  being  subject  to  220  volts,  while  the  other 
half  would  burn  properly. 

If  a  short  circuit  occurs,  say  at  c,  Figure  134,  on  one  side 
of  a  3-wire  system  and  blows  the  neutral  fuse  on  that  side  of 
the  circuit,  we  shall  have  220  volts  on  the  lamps  on  the  oppo- 
site side.  This  will  quickly  burn  them  out.  Most  of  these 


C    6    6    6     fe 


oooooooooooo 


a 


Figure  134 


troubles  are  avoided  to  some  extent  by  the  use  of  such  branch 
cutouts  as  shown.  This  confines  trouble  of  this  kind  to  the 
mains. 

On  any  system  having  a  neutral  wire  or  a  wire  on  one  side 
grounded,  if  a  ground  en  either  of  the  other  wires  occurs,  the 
trouble  can  be  temporarily  remedied  by  simply  changing  the 
two  wires  of  that  circuit  at  the  cutout.  This  will  trans- 
fer the  ground  to  the  side  already  grounded,  so  that  it  will 
not  interfere  with  operation.  The  ground  must,  however,  be 
cleared  up  at  once  as  no  grounding  is  ever  allowed  inside  of 
any  building. 

When   strip  cutouts  are   set  horizontally  and   there   is  no 


220  MODERN    ELECTRICAL  CONSTRUCTION. 

bridge  between  opposite  polarities,  there  will  be  the  possibility 
of  a  partially  melted  upper  fuse  sagging  down  and  forming  a 
short  circuit. 

On  panel  boards  where  fuses  are  set  too  close  together,  the 
heat  of  one  fuse  while  blowing  will  often  blow  the  next  fuse 
above  it. 

If  large  fuses  are  enclosed  in  small  and  very  tight  cabi- 
nets, the  vapors  formed  by  blowing  will  often  cause  short 
circuits. 

Before  installing  fuses  in  a  "loaded"  circuit,  it  is  advisable 
to  disconnect  as  many  lights  and  other  devices  as  possible.  If 
there  is  a  main  switch  this  can  easily  be  done.  If  there  is  no 
such  switch  on  that  part  of  the  system,  the  task  of  placing 
fuses  is  somewhat  hazardous ;  for  at  the  very  instant  that  the 
second  fuse  touches  its  terminal  a  great  rush  of  current  will 
flow.  If  there  happens  to  be  a  "short"  on  the  line  both  fuses 
will  probably  blow  and  may  burn  the  operator's  hands  and 
face  severely.  In  order  to  avoid  this,  extremely  careful  manip- 
ulation is  necessary.  The  first  fuse  can  be  placed  without 
any  difficulty,  as  there  will  be  no  current  flow  unless  the  cir- 
cuits are  grounded.  Before  attempting  to  place  the  second 
fuse  the  circuits  may  be  tested  for  "shorts"  by  placing  a 
"jumper"  (a  piece  of  wire  heavy  enough  so  that  it  will  not 
be  heated  by  the  current  it  is  to  carry)  with  the  ends  on  the 
other  fuse  terminals.  This  "jumper"  will  complete  the  cir- 
cuit and,  if  all  is  in  order  the  lights  will  burn.  If  there  are 
two  men,  one  may  hold  the  jumper  while  the  other  places  the 
fuse,  but  it  should  be  placed  as  quickly  as  possible,  especially 
if  the  circuit  has  a  motor  load,  for  these  will  be  started  very 
soon  after  the  lights  come  on  and  will  greatly  increase  the 
current.  If  there  is  but  one  man  the  jumper  may  be  tem- 
porarily fastened  to  the  mains. 

A  jumper  is  not  absolutely  necessary  even  with  large  fuses, 
for  if  the  last  contact  is  made  quickly  and  held  steady,  there 


PRACTICAL  HINTS.  221 

will  be  very  little  arcing;  one  should,  however,  provide  all  pro- 
tection possible.  If  a  piece  of  asbestos  is  at  hand,  it  may  be 
used  to  cover  the  fuses,  so  as  to  protect  the  hands  and  face 
from  melted  metal. 

Before  attempting  to  re-fuse  a  circuit,  note  condition  of 
cutout  block.  If  there  is  evidence  of  a  great  flash,  it  is  very 
likely  that  the  fuse  was  blown  by  a  short  circuit.  If  the 
blowing  was  caused  by  a  slight  overload  or  loose  contact,  the 
destructive  effect  will  be  much  less. 

Much  trouble  can  be  prevented  by  cleaning  terminals  of 
fuse  blocks  occasionally  and  going  over  nuts  and  screws  to 
see  that  they  are  tight. 

In  Figure  135,  a  shows  the  proper  way  of  connecting  small 
wires  into  such  terminals.  This  method  prevents  the  screw 
from  cutting  into  the  main  wire  and  allowing  it  to  break. 

A  wire  should  always  be  bent  around  the  binding  post  of 
switch  or  cutout  in  the  direction  in  which  the  nut  which  is  to 


•"b  "C 

Figure  135 

hold  it  must  turn  to  be  fastened  as  in  c.  If  a  wire  is  not  long 
enough  to  be  bent  around  the  post  or  screw,  a  small  piece  of 
wire  should  be  placed  opposite  it  so  as  to  give  a  level  bearing 
to  nut  or  washer.  See  b. 

Plug  cutouts  having  their  metal  parts  projecting  above  the 
porcelain,  as  shown  at  d,  should  be  connected,  whenever  pos- 
sible, so  that  these  metal  parts  are  dead  when  fuses  are  with- 
drawn. This  will  prevent  many  accidental  short  circuits. 

The  positive  and  negative  wires  of  a  circuit  can  easily  be 
determined  by  immersing  both  wires  in  a  little  water,  keeping 


222  MODERN   ELECTRICAL  CONSTRUCTION. 

them  an  inch  or  so  apart.    Small  bubbles  will  soon  appear  at 
the  negative  wire. 

If  an  arc  lamp  has  been  properly  connected,  the  upper  car- 
bon will  be  heated  much  more  than  the  lower  and  will  remain 
red  longer.  An  arc  lamp  improperly  connected  is  said  to  be 
burning  "upside  down"  and  will  at  once  manifest  itself  by  the 
strong  light  thrown  against  the  ceiling. 

It  is  very  often  found  necessary  to  determine  the  capacity 
of  a  cable  which  is  already  installed  and  where  it  is  impossible 
to  get  at  the  separate  wires  of  which  it  is  formed.  As  cables 
are  usually  made  up  in  a  uniform  manner,  as  shown  in  the 
table  below,  their  capacity  can  be  determined  by  the  following 
method :  To  find  the  number  of  circular  mils  in  a  cable  made 
up  of  wires  of  uniform  size.  Measure  diameter  of  cable, 
count  number  of  wires  in  outside  layer,  and,  referring  to  the 
table  below,  find  the  same  number  in  the  first  column ;  divide 
the  diameter  of  cable  by  the  number  set  opposite  this  in  the 
second  column.  This  will  give  the  diameter  of  each  wire. 
Multiply  this  diameter  by  itself  and  then  by  the  number 'of 
wires  contained  in  cable  as  given  in  the  third  column.  All 
measurements  should  be  expressed  in  mils  (1/1,000  inch)  and 
the  result  will  be  the  circular  mils  contained  in  cable. 
Outside  layer 


6  wires 

3 

times  diameter 

7  wires 

in  cable 

12 

5 

19 

18 

'7 

«• 

37        " 

ii     ii 

24 

9 

" 

61 

"     " 

30 

11 

"              " 

91 

"     " 

36 

18 

" 

127 

42 

15 

169        " 

"     " 

The  various  figures  in  Figure  136  are  designed  to  show  how 
many  single  wires  may  be  run  in  one  conduit.  Under  each 
figure  is  given  a  number  which,  if  multipled  by  the  diameter 
of  the  wire  to  be  used  will  give  the  smallest  diameter  of 
tube  which  can  contain  the  corresponding  number  of 
wires.  Thus,  for  instance,  if  12  wires  are  run  through 


PRACTICAL   HINTS 


224  MODERN   ELECTRICAL  CONSTRUCTION. 

one  tube  or  conduit,  the  diameter  of  that  conduit 
must  be  at  least  4  1/3  times  as  great  as  the  diame- 
ter of  the  wire  to  be  used.  Each  figure  illustrates 
the  amount  of  spare  room  the  corresponding  number  of  wires 
leave,  and  it  is  necessary  to  use  considerable  judgment.  Long 
runs  will  require  more  space,  especially  if  the  wires  be  quite 
large.  Much  also  depends  upon  the  nature  of  the  insulation 
and  the  temperature.  The  figures  are  believed  to  be  correct 
for  single  wires  and  can  be  followed  for  twin  wires,  as  the 
same  number  of  conductors  arranged  that  way  will  not  occupy 
as  much  space  as  single  wires.  The  actual  diameter  of  lined 
and  unlined  conduits  are  given  in  another  table  and  may  be 
referred  to.  The  best  way  to  accurately  determine  the  diam- 
eter of  small  wire  consists  in  cutting  a  number  of  short  pieces 
and  laying  them  together,  then  measuring  over  all  and  divid- 
ing the  measurement  by  the  number  of  wires. 


TRICKS  OF  THE  TRADE. 

Cases  have  been  known  where  it  was  requested  to  replace 
single  pole  switches  by  double  pole,  that  the  single  pole  switch 
was  replaced  as  requested,  but,  instead  of  running  both  wires 
through  it  as  required,  only  one  wire  had  been  properly 
brought  into  it  and  the  other  two  binding  posts  filled  out  with 
short  pieces  of  wire  calculated  to  deceive  the  inspector.  A 
test  to  detect  this  without  disconnecting  the  switch  is  easily 
made.  By  reference  to  Figure  137  it  will  be  seen  that  if  a 
double  pole  snap  switch  is  properly  connected,  current  can 
be  felt  if  the  points  a  and  b  are  touched  with  moistened  fin- 
gers. If  the  switch  is  connected  single  pole,  current  can  be 
felt  at  b  and  c,  when  the  switch  is  open,  only. 

On  one  occasion  a  wireman  had  run  some  wires  on  insu- 
lators along  a  ceiling  and  instead  of  soldering  joints  had  care- 


THICKS  OF  THE  TRADE.  225 

fully,  in  many  places  above  the  joints,  smoked  the  ceiling  with 
a  candle  in  order  to  deceive  an  inspector. 

In  several  cases  where  an  "over-all"  test  of  insulation  re- 
sistance was  made,  meter  loops  which  had  been  run  in  con- 
tinuous pieces  were  found  with  the  wire  "nicked"  with  a  knife 
and  then  broken,  leaving  the  insulation  nearly  intact,  but  the 
circuit  open.  A  similar  trick  is  often  worked  with  the  ground 
wire  of  ground  detectors. 

In  other  cases  plugs  with  fuses  removed  were  put  in 
"bad"  circuits.  In  one  case  the  real  circuit  wires  (concealed 


Figure  137  Figure  138 

work)  were  disconnected  from  cutouts  and  pushed  back  into 
the  wall  and  short  pieces  connected  instead. 

In  another  case  where  wire  not  up  to  requirements  had 
been  used  and  condemned,  this  wire,  being  run  between  joists 
and  concealed  by  plastering,  was  pushed  back  and  short 
pieces  of  approved  wire  stuck  in  at  outlets. 

Sometimes  in  fished  work  after  inspection  the  long 
pieces  of  loom  reaching  from  outlet  to  outlet  are  withdrawn 
and  short  pieces  at  the  outlets  substituted. 

Lamp  butts  with  wire  terminals  twisted  together,  or  a 
strand  of  wire  from  lamp  cord  twisted  around  the  base  as 
shown  in  Figure  138  and  screwed  into  the  cutout  are  often 
used  in  place  of  fuses.  The  strand  of  cord  is  sometimes  used 
to  help  out  a  fuse  plug  on  an  overloaded  circuit. 


226 


MODERN   ELECTRICAL  CONSTRUCTION. 


Table  cf  Carrying  Capacity  of  Wires. 

The  following  table,  showing  the  allowable  carrying  ca- 
pacity of  copper  wires  and  cables  of  ninety-eight  per  cent  con- 
ductivity, according  to  the  standard  adopted  by  the  American 
Institute  of  Electrical  Engineers,  must  be  followed  in  placing 
interior  conductors. 

For  insulated  aluminum  wire  the  safe  carrying  capacity 
is  eighty-four  per  cent  of  that  given  in  the  following  tables 
for  copper  wire  with  the. same  kind  of  insulation 

TABLE  NO.  I. 


Table  A. 
Rubber 
Insulation. 
See  No.  41. 
B.  &  S.  G.      Amperes. 
18  3.... 
16...        6... 

Table  B. 
Other 
Insulations. 
SeeNos.  42  to  44. 
Amperes.  Circular  Mils. 
5  1.624 
8  2.583 

14. 

12 

16 

4  107 

12  

17.  .  . 

6,530 

10  
8 

24  
33 

46 

.  .  10,380 
16  510 

6  
5  

.   46  
54.  ... 

...   65  
77  

.  .  26,250 
.  .  33,100 

4  
3  

65  
76.  .  . 

92  
.  110... 

.  .  41,740 
.  .  52,630 

2  
1  
0  

90  
.  107  
.  127.  .  .  . 

...  131  
.  .  .  156  
.  .  .  185  

.  .  66,370 
.  .  83,690 
.  .105,500 
.  .133,100 
.  .167,800 
.  .211,600 

00  
000 

.  150  
177 

...  220  

262 

0000  
Circular  Mils. 
200,000  
300,000  
400,000  
500,000  
600,000  
700,000  

.  210  

.  200  
.  270  
.  330  
.  390.... 
.  450  
.  500.  .  .  . 

...  312  

.  300 
...  400 
...  500 
.  ...  590 
...  680 
760 
840 
...  920 
1,000 
080 
150 

800,000  
900,000  
1,000,000  
1,100,000  
1,200,000.  .  . 

.  550  
.  600.... 
.  650  
.  690  
.  730... 

1  300  000 

770 

220 

1,400,000  
1,500,000  
1  600  000 

.  810  
.  850  
890 

290 
1,360 
430 

1,700.000  
1,800,000  
1,900,000  
2,000,000  

.  930  
.  970  
.1,010  
.1,050  

490 
550 
610 
....1,670 

TABLES.  227 

The  lower  limit  5s  specified  for  rubber-covered  wires  to 
prevent  gradual  deterioration  of  the  high  insulations  by  the 
heat  of  the  wires,  but  not  from  fear  of  igniting  the  insulation. 
The  question  of  drop  is  not  taken  into  consideration  in  the 
above  tables. 

The  carrying  capacity  of  Nos.  16  and  18,  B.  &  S.  gage  wire 
is  given,  but  no  smaller  than  No.  14  is  to  be  used,  except  as 
allowed  under  Nos.  24  v  and  45  b. 


WIRING  TABLES. 

The  wiring  tables,  II-VI,  are  arranged  in  the  following 
manner:  For  each  size  of  wire  and  voltage  considered  there 
is  given  (under  the  proper  voltage  and  opposite  the  number 
of  the  wire  under  the  heading  B.  &  S.)  the  distance  it  will 
carry  1  ampere  at  a  loss  designated  at  top  of  page. 

The  same  wire  will  carry  2  amperes  only  half  as  far  at  the 
same  percentage  of  loss  and  again  will  carry  I  ampere  twice 
as  far  at  double  the  percentage  of  loss. 

From  these  facts  we  deduce  the  rule  of  these  tables,  which 
is:  Multiply  the  distance  in  feet  (one  leg  only)  by  the  num- 
ber of  amperes  to  be  carried.  Take  the  number  so  obtained 
and  under  the  proper  voltage  find  the  number  nearest  equal  to 
it.  Opposite  this  number,  under  the  heading  B.  &  S.,  will  be 
found  the  size  of  wire  required.  To  illustrate :  We  have  22 
amperes  to  carry  a  distance  of  135  feet  and  the  loss  to  be  al- 
lowed is  3  per  cent  at  110  volts.  We  therefore  multiply  135  X 
22  =  2970,  and  turning  to  table  TV.,  which  is  figured  for  3  per 
cent  loss,  follow  downward  in  the  column  under  110  until  we 
reach  the  number  nearest  equal  to  2970,  which,  in  this  case,  is 
.3180  corresponding  to  a  No.  7  wire.  With  this  wire  our  loss 
will  be  slightly  less  than  3  per  cent,  while  with  No.  8  it  would 
be  somewhat  in  excess  of  3  per  cent. 

For  three-wire  systems  using  110  volts  on  each  side  the 
column  marked  220  volts  should  be  used.  The  column  marked 
440  volts  is  provided  for  three-wire  systems  using  220  volts 


228  MODERN   ELECTRICAL   CONSTRUCTION. 

on  each  side.     The  sizes  determined  will  be  correct  for  all 
three  wires  in  both  cases. 

The  columns  at  the  right,  marked  motors,  are  arranged 
in  the  same  way,  the  only  difference  being,  for  greater  con- 
venience, they  are  figured  in  horse-power  feet  instead  of  am- 
pere feet.  For  this  reason  we  multiply  the  distance  in  feet 
by  the  number  of  horse-power  to  be  transmitted  and  divide 
by  tfie  percentage  of  loss,  all  other  operations  remaining  the 
same  as  under  lights.  When  any  considerable  current  is  to 
be  carried  only  a  short  distance  the  wire  indicated  by  the  de- 
sired loss  will  very  likely  not  have  sufficient  carrying  capacity ; 
it  is,  therefore,  always  necessary  to  consult  the  table  of  carry- 
ing capacities. 


RULE  FOR  WIRING  TABLES. 

For  lights,  find  the  ampere  feet  (one  leg)  and  under  the 
proper  voltage  find  the  number  equal  to  this  or  the  next 
larger;  opposite  this  number,  in  the  column  marked  B.  & 
S.,  will  be  found  the  size  of  wire  required. 

For  motors,  proceed  in  the  same  way,  using  horse- 
power feet  instead  of  ampere  feet. 

For  alternating  currents,  the  results  obtained  by  multi- 
plying the  amperes  (or  horse-power)  by  the  feet,  should 
be  multiplied  by  the  following  factors: 

1.1  for  single-phase  systems,  all  lights. 

1.5  for  single-phase  systems,  all  motors. 

For  two-phase,  four-wire,  or  three-phase,  three-wire 
systems,  each  wire  need  be  only  one-half  as  large  as  for 
single-phase  systems  and  the  number  obtained  may,  there- 
fore, be  divided  by  two. 


229 


PI 


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230 


MODERN   ELECTRICAL  CONSTRUCTION. 


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232 


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MODERN   ELECTRICAL  CONSTRUCTION. 

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234  MODERN   ELECTRICAL  CONSTRUCTION. 

It  is  often  necessary  to  reinforce  mains  which  have  become 
overloaded.  It  is  quite  usual  though  often  very  incorrect,  to 
choose  by  the  table  of  carrying  capacities  a  wire  of  such  size 
that  the  rated  capacity  of  it  and  the  wire  to  be  re-enforced 
shall  be  equal  to  the  load.  Small  wires  have  proportionately 
a  much  greater  radiating  surface  than  larger  ones  and  there- 
fore their  carrying  capacity  is  proportionally  greater.  In  order 
that  a  wire  connected  in  parallel  with  another  wire  shall  carry 

C.  M.  X  a 
a  certain  current,  its  circular  mils,  must  be  equal  — 

.A. 

where  C.  M.  stands  for  the  cross-section  of  the  larger  wire  in 
circular  mils  and  A  for  the  current  to  be  carried  by  it,  while 
a  is  the  current  to  be  carried  by  the  extra  wire.  Table  No. 
VII  is  calculated  from  this  rule  and  shows  the  size  of  wire 
necessary  to  re-enforce  another  overloaded  to  a  certain  per 
cent  as  indicated  in  the  top  row.  For  instance,  a  0000  wire 
overloaded  40  per  cent  requires  re-enforcement  by  a  No.  1 ;  a 
No.  3  wire  overloaded  20  per  cent  requires  a  No.  10  wire. 
Where  large  wires  are  re-enforced  in  this  way  by  smaller  ones 
great  care  must  be  taken  that  the  larger  wire  cannot  be  acci- 
dentally broken  or  disconnected,  since  in  such  a  case  the  whole 
load  would  be  forced  over  the  smaller  wire  and  would  likely 
result  in  a  fire.  The  two  wires  should  be  securely  soldered 
together. 

TABLE   NO.   VII. 


Am- 

peres. 

B.  &S. 

10% 

20 

30 

40  50 

60 

70 

80 

90 

100 

210 

0000 

6 

4 

2 

1   0 

00 

000 

000 

0000 

0000 

177 

000 

8 

5 

3 

2   1 

0 

00 

000 

000 

000 

150 

00 

9 

6 

4 

3   2 

1 

0 

0 

00 

00 

127 

0 

10 

7 

5 

4   3 

2 

1 

1 

0 

0 

107 

1 

10 

8 

6 

5   4 

3 

2 

2 

1 

1 

90 

2 

11 

9 

7 

6   5 

4 

3 

3 

2 

2 

76 

3 

12 

10 

8 

7   6 

5 

4 

4 

3 

3 

65 

4 

14 

11 

9 

8   7 

6 

5 

5 

4 

4 

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236 


MODERN    ELECTRICAL   CONSTRUCTION. 
DIMENSIONS  OF  COPPER  WIRE 


K 

S*% 

l«5 

3|| 

Q5S 

lit 
IbM 

<'5Su 

Weights 

ll 

II 

1000  feet 

Mile 

0000 

460. 

211,600. 

641. 

3,382. 

.051 

000 

410. 

168,100. 

509. 

2,687. 

.064 

00 

365. 

133,225. 

403. 

2,129. 

.081 

o 

325. 

105,625. 

320. 

1,688. 

.102 

1 

289. 

83,521. 

253. 

1,335. 

.129 

2 

258. 

66,564. 

202. 

1,064. 

.163 

3 

229. 

52,441. 

159. 

838. 

.205 

4 

204. 

41,616. 

126. 

665. 

.259 

5 

182. 

33,124. 

100. 

529. 

.326 

6 

162. 

26,244. 

79. 

419. 

.411 

7 

144. 

20,736. 

63. 

331. 

.519 

8 

128. 

16,384. 

50. 

262. 

.654 

9 

114. 

12,996. 

39. 

208. 

.824 

10 

102. 

10,404. 

32. 

166. 

1.040 

11 

91. 

8,281. 

25. 

132. 

1.311 

12 

81. 

6,561. 

20. 

105. 

1.653 

13 

72. 

5,184. 

15.7 

83. 

2.084 

14 

64. 

4,096. 

12.4 

65. 

2.028 

15 

57. 

3,249. 

9.8 

52. 

3.314 

16 

51. 

2,601. 

7.9 

42. 

4.179 

17 

45. 

2,025. 

6.1 

32. 

5.269 

18 

40. 

1,600. 

4.8 

25.6 

6.645 

19 

36. 

1,296. 

3.9 

20.7 

8.617 

20 

32. 

1,024. 

3.1 

16.4 

10.566 

21 

28.5 

812.3 

2.5 

13. 

13.283 

22 

25.3 

640.1 

1.9 

10.2 

16.85 

23 

22.6 

510.8 

1.5 

8.2 

21.10 

24 

20.1 

404. 

1.2 

6.5 

26.70 

25 

17.9 

320.4 

.97 

5.1 

33.67 

26 

15.9 

252.8 

.77 

4. 

42.68 

27 

14.2 

201.6 

.61 

3.2 

53.52 

28 

12.6 

158.8 

.48 

2.5 

67.84 

29 

11.3 

127.7 

.39 

2. 

84.49 

30 

10. 

100. 

.3 

1.6 

107.3 

31 

8.9 

79.2 

.24 

1.27 

136.2 

3? 

8. 

64. 

.19 

1.02 

168.5 

33 

7.1 

50.4 

.15 

.81 

214.0 

34 

6.3 

39.7 

.63 

271.7 

35 

5.6 

31.4 

!095 

.5 

343.6 

36 

5. 

25. 

.076 

.4 

431.6 

TABLES. 


237 


Table  giving  the  outside  diameters  of  rubber  covered  wires  for  use  on 
voltages  less  than  600. 


Size 
B.  &S 
Gauge 

Solid 
Wire 
Single 
Braid 

Solid      Strand- 
Wire     ed  Wire 
Double    Single 
Braid       Braid 

Strand- 
ed Wire 
Double 
Braid 

Solid 
Twin  Wire 

Stranded 
Twin  Wires 

0000      47-64 

54-64  ;   52-64 

59-64 

54-64x101-64 

59-64x111-64 

000 

41-64 

46-64      48-64 

55-64 

46-64x  87-64 

55-64x103-64 

00 

38-64 

43-64       43-64       4-i  64 

43-64x  81-64      48-64x  91-64 

0 

36-64 

40-64      40-64       45-64 

40-64x  75-64      45-64x  85-64 

1 

33-64      37-64 

37-64 

42-04 

37-64x  70-64 

42-64x  79-64 

2 

29-64  !  33-64 

32-64 

37-64 

33-64x  62-64  '  37-64x  69-64 

3 

27-64  !   31-64      30-64       34-64 

31-64x  58-64      34-64x  64-64 

4 

25-64      29-64 

27-64 

31-64 

29-64.X  54-64      31-64x  58-64 

5 

24-64      28-64 

28-64x  52-64 

6 

22-64  I  26-64 

24-64 

-'8-64 

26-64x  49-64 

28-64x  52-64 

8 

18-64  '  22-64 

20-64 

23-64 

22-64x  41-64 

23-64x  42-64 

10 

16-64      20-64 

18-64       21-64 

20-64x  37-64      21-64x  38-64 

12 

15-64      19-64 

16-64       20-64 

19-64x  35-64      20  64x  36  64 

14 

14-64  1    18-64 

15-64 

19-64 

18-64x  33-64       19-64x  34-64 

16 

10-64      13-64 

13-64x  24-64 

18 

&-64  !   12-64 

12-64x  22-64 

Table  giving  the  outside  diameters  of  rubber  covered 
Voltages  between  600  and  3500. 


i-ires  for  use  on 


Sue 
B.  &S. 
Gauge 

Solid 
Wire 
Single 
Braid 

Solid 
Wire 
Double 
Braid 

Strand- 
ed Wire 
Single 
Braid 

Strand- 
ed Wire            Solid 
Double       Twin  Wire 
Braid 

Stranded 
Twin  Wire 

0000      49-64 

56-64 

53-64 

61-64   |   56-64x105-64 

61-64x114-64 

000 

46-64 

53-64 

50-64 

57-64 

53-64x  99-C>4      57-64x107-64 

00 

41-64 

46-64    !    47-64    1    53-64      46-64x  87-64      53-64x  99-64 

0 

38-64 

43-64       42-64       46-64      43  64x  81-64      46-64x  88-64 

1 

35-64 

40-64 

39-64 

43-64 

40-64x  75-64      43-64x  82-64 

2 

33-64 

38-64 

36-64 

40-64 

38-64x  71-64      40-64x  76-64 

3 

31-64 

36-64 

34-64       38-64   '  36-64x  67-64      38-64x  72-64 

4 

29-64  !   33-64 

31-64 

35-64  i   33-64x  62-64      35-64x  66-64 

5 

28-64 

32-64 

32-64x  60-64 

6 

27-64      31-64 

28-64 

32-64 

31-64x  58-64      32-64x  60-64 

8 

24-64 

28-64 

26-64 

30-64 

28-64x  52-64      30-64x  56-64 

10 

22-64      26-64 

24-64       28-64 

26-64x  48-64      28-64x  52-64 

12 

21-64 

25-64 

22-64       26-64 

25-64x  46-64 

26-64x  48-64 

14 

20-64       24-64 

21-64       25  64 

24-64x  44-64      25-64x  46-64 

mam 

these  dimensions  as  me  panic  size  wuc  u-  o 
often  varies  considerably  in  outside  diameter. 


238 


MODERN   ELECTRICAL  CONSTRUCTION. 


Outside  Diameters  of  Rubber 
Covered  Cables. 


Capacity  in 
Cir.  Mils. 

Diameter 
over  Braid 

1,500,000 

113-64 

1,250,000 

107-64 

1,000,000 

97-64 

950,000 

95-64 

900,000 

94-64 

850,000 

93-64 

800,000 

89-64 

750,000 

87-64 

700,000 

83-64 

650,000 

81-64 

600,000 

79-64 

550,000 

76-64 

500,000 

73-64 

450,000 

68-64 

400,000 

66-64 

350,000 

64-64 

300,000 

61-64 

250,000 

59-64 

Dimensions  of  Unlined  Conduit. 


Nominal 
Internal 

Actual 
Internal 

Actual    iThick- 
External  'ness  of 

Diam. 

Diam. 

Diam. 

Walls 

Inches. 

Inches. 

Inches. 

Nearest 

64th 

17-64 

26-64 

4-64 

23-64 

35-64 

5-64 

31-64 

43-64 

6-64 

40-64 

54-64 

6-64 

52-64 

67-64 

7-64 

67-64 

84-64 

8-64 

•  i 

88-64 

106-64 

9-64 

H 

103-64 

122-64 

9-64 

2 

132-64 

152-64 

10-64 

5ft 

157-64 

184-64 

13-64 

3 

196-64 

224-64 

13-64 

Outside  Diameters  of  Weather- 
proof Wire. 


Size  of 
Wire 

Outside  Diameters. 

Solid 

Stranded 

i  fwin  fwv^ 

1  ,IHH),UUU 

900,000 



108—64 
103-64 

M  )(),()(  III 



100-64 

700,000 



94-64 

t  »O(  I  (MM) 

QC_£»J 

sooiooo 



S.)    h-1 

80-64 

450,000 



76-64 

400,000 



73-64 

350,000 



64-64 

300,000 



62-64 

.'.-,(  l.i  i(  Id 



58-64 

0000 

50-64 

55-64 

000 

47-64 

51-64 

00 

39-64 

43-64 

0 

36-64 

39-64 

32-64 

35-64 

2 

30-64 

33-64 

3 

27-64 

30-64 

4 

25-64 

28-64 

5 

22-64 

24-64 

6 

20-64 

22-64 

8 

17-64 

18-64 

10 

16-64 

12 

14-64 

14 

12-64 

16 

10-64 

18 

8-64 

Dimensions  of  Lined  Conduit 


Nominal 
Internal 
Diameter 
Inches 

Actual 
Internal 
Diameter 
Inches 

Actual 
External 
Diameter 
Inches 

F 

I1 

32-64 
45-64 
58-64 
80-64 
90-64 
115-64 
144-64 
176-64 

54-64 
67-64 
84-64 
106-64 
122-64 
152-64 
184-64 
224-64 

TABLES. 
DIMENSIONS  OF   PORCELAIN   KNOBS. 


239 


Trade 
No. 

Height 

Diameters 

H 

ole 

Groove 

H$ 

htof 
ire 

0 

I* 

3 

2J 

] 

- 

i 

" 

1 

i 

2 

2 

2 

; 

: 

3 

11 

2 

j 

3i 

2 

2 

! 

4 

ft 

1* 

5 

1 

i* 

5J 

JL 

i 

7 

J 

z 

9 

| 

1 

.. 

10i 

1 

it 

DIMENSIONS   OF   GLASS   KNOBS. 


Trade 
Number 

Keif 
1 

i] 
ii 

2 
2 

3] 

'ht              Width 

Size  of 
Hole 

Size  of 
Groove 

j1 

7 
8 

f 

2 
2J 

1"  cable 

SIZES  OF   PORCELAIN    TUBES. 


Internal 
Diameter 
Inches 

Shortest 
Length 
Obtainable 

Greatest 
Length 
Obtainable 

Outside 
Diameter 

f 

| 

1 
1< 

24 
24 
24 
24 
24 
24 

1 

11 

2< 

24 

IT~$ 

i! 

2^ 

94 

2-j^- 

ii 

2^ 

24 

2iV 

2f 

2^ 

24 

2H 

2J 

2^ 

2^ 

24 

3U 

DIMENSIONS   OF  MOULDINGS. 


Siz 

B  of  Groove 

Size  of  Wire 

Size  of  Groove 

7-32 
5-16 
13-32 
9-16 

14-12  B.  &  S. 
10-  8  B.  &  S. 
6-5-4  B.  &  S 
32  1-0  B.  &  S. 

3-4 

7-8 
1 
1    1-4 

0-0000  Stranded 
250.000  C.  M. 
500.000  C.  M. 
750.  000  C.  M. 

240  MODERN   ELECTRICAL   CONSTRUCTION. 

DIMENSIONS  OF  CLEATS. 


ONE-WIRE  CLEATS. 
DUOGAN  CLEAT. 

No.  4  holds  wires  16-8  B.  &  S. 

No.  7       -         "     6-2       " 

No.  5       "         "     2-00 

No.  6       "         "     000-300,000  C  M. 

No.  8       "         "     400.000-800,000  C.  M. 

No.  0       "         "     900,000- 1, 200,000  C.  M. 

BRDNT  CI.EAT. 
Stand. 
Number  Width  Length  Groove 

328  |  2  <        holds  wires 16-5  B.  &  S 

329  1  2i  i  "'       " 8-3 

331  if         2|  H  "         "     3-00 

330  1J         2}  i  "         "     4-1 

332  11         21  H  "         "     0-0000 

Two  AND  THREE-WIRE  CLEATS. 
BHONT. 

No.  334   2-wire  holds  wires    16-8  B.  &  S- 

No.  337   3  wire      "         "        16-8  B.  &  S 

DOOGAN. 

No.  3       2-wire  holds  wires    16-8  B.  &  8. 

No.  2       2-wire      "         "        ' 6-00  B.  &  S. 

No.  1       3  wire      "  ...  16-8  B.  &  S. 


PASS  &  SEYMOUR. 

No.  A-3     2-wire  holds  wires  14-12  B.  &  S.j 

No.  3         2-wire      "         "  14-  6  B.  &  8- 

No.  A-43  3-wire       "         "  14-12  B.  &  S. 

No.  43       3-wire      "  ...  14-  6  B.  &  3. 


APPROXIMATE. 


Trade  Numbe 

Diameter  in 
fractions 

0 

ri. 

3 

V 

«| 

r 

5 

A 

6 

7 

iYi 

8 

rira 

9 
in 

n 

JU 

11 

II 

12 

14 

13 

¥• 

14 

np 

15 

i4 

16 

* 

17 

94 

18 

1 

— 

DIMENSIONS  OF  COMMON  NAILS.     APPROXIMATE. 


Trade 
Number 

—  —  —  —  — 

Diameter  in 
Fractions 

Nearest    B.  &  S. 
Gauge 

Length  in            N0. 
Inches            per  lb 

2d 
3d 

ill 

13 

1                           crc 

4d 

w 

12 

U                   565 

5d 

y 

18 

6d 

y 

10                             U                    ;'70 

7d 
8d 

£ 

9                            ^                    ifO 

9d 
lOd 

s 

8 
8 

22 

105 
95 

12d 

Jl» 

7 

70 

Ifld 

nn 

C                           3} 

60 

20d 

ft 

6                           3i 

50 

•  

1  •  —  

4                            4 

30 

FINE  NAILS 


242 


MODERN   ELECTRICAL  CONSTRUCTION. 
RATING  OF  MOTORS. 
FULL  LOAD  CURRENTS. 


H.  P. 

110  VOLTS 

220  VOLTS 

500  VOLTS 

1  9 

.95 

.42 

2  7 

1.35 

.62 

5. 

2.50 

1.15 

7.5 
9.2 

3.75 
4.60 

1.70 
2.10 

2 
3 
4 
5 

7i 

17.5 
24.6 
32. 
40. 
57. 

8.75 
12.30 
16. 
20. 
28.5 

4. 
5.60 
7.50 
9.^0 
13. 

10 
15 
20 

76. 
110. 
144. 

38. 
55. 
72. 

17.5 
25. 
34. 

25 
30 

176. 
210. 

88. 
105. 

49. 

35 
40 

45 

250. 
280. 
320. 

125. 
140. 
160. 

57. 
65. 
75. 

50 

60 

350. 
430. 

175. 
215. 

100. 

75 
100 
125 
150 

520. 
700. 
880. 
1056. 

260. 
350. 
440. 
530. 

120. 
160. 
210. 
245. 

175 
200 

1230. 
1400. 

615. 
700. 

325. 

RATING  OF  INCANDESCENT  LAMPS. 


110  VOLTS 

220  VOLTS 

C.  P. 

Watts 

Amperes 

C.  P. 

Watts 

Amperes 

4 

18 

.16 

8 

36 

.16 

6 
8 
10 
12 
16 
20 

24 
30 
35 
40 
56 
70 

.22 
.27 
.32 
.36 
.51 
.64 

10 
16 
20 
24 
32 
50 

45 
64 
76 
90 
122 
190 

.29 
.35 
.41 
.55 
.86 

24 

84 

.76 

32 

112 

1.00 

50 

175 

1.60 

TABLES.  243 

The  Hewitt-Cooper  Mercury  Vapor  lamp  requires  a  current  of  about  2.5 

amperes. 

The  Nernst  lamp  consumes  88  watts  per  glower;   for  a  6  glower,  110  volt 

lamp,  about  4.8  amperes. 

Series  miniature  lamps,  operated  8  in  series,  on  110  volts,  require  a  current 

of  about  .33  amperes  for  1  candle  power  lamps,  and  1  ampere  for  3  candle 

power  lamps. 


Tables    showing    the  currents  which  will    fuse  wires  of   different  sub- 
stances. 


B.  &S. 
Gauge 

Hiai.i. 

Copper 

Aluminum 

German 
Silver 

Iron 

10 

102. 

333. 

246.5 

170. 

102.3 

12 

81. 

236. 

174.4 

120.5 

72.6 

14 

64. 

165.7 

122.8 

84.6 

50.9 

16 

51. 

117.7 

87.1 

60.1 

36.1 

18 

40. 

81.9 

60.7 

41.8 

25.2 

20 

32. 

58.5 

43.4 

29.9 

18. 

22 

25.3 

41.1 

30.5 

21.0 

12.4 

24 

20. 

28.9 

21.5 

14.8 

8.9 

26 

16. 

20.7 

15.3 

10.6 

0.4 

28 

12.6 

14.5 

10.7 

7.4 

4.5 

30 

10. 

10.2 

7.6 

5.2 

3.1 

32 

8. 

7.3 

5.4 

3.7 

2.3 

34 

6.3 

5.1 

3.8 

2.6 

1.6 

36 

5. 

3.6 

2.7 

1.8 

1.1 

INDEX 


Page. 
J-13 


Acid    Fumes 76-137 

Alternating  Current  System :55 

Amperes    13 

Arc  Lamps,  Construction  of 209 

Arc  Lamps,  Installation  of 108-113-167 

Arc  Lamp  Switches 109 

Armored    Cable 181 

Base  Frames,  Generators  and  Motors 47-63 

Batteries,  Storage  or  Primary 27-76 

Bells 19 

Binding  Screws,  Not  to  Bear  Strain 166 

Bonds,  Rails  in  Car  Houses 169 

Boxing,   Where   Necessary 111-133-171 

Burrs  and  Fins,  Fixture  Work 161 

Bushings  for  Wires 97-185 

Bushings,  Lamp  Sockets 166 

Bus  Bars 52-54 

Cabinets  for  Cut-Outs 123-202 

Cable,    Armored 181 

Calculation  of  Wires 40 

Care  and  Attendance 59 

Car    Houses 169 

Carrying  Capacity  Table 226 

Car  Wiring 169 

Ceiling  Fans 75-160 

Central    Stations 47 

Circular  Mil 40 

Circuit  Breakers,  Construction  of 194 

Circuit  Breakers,   Installation  of 51-73-76-105-114-123 

Circuit,  Open 9 

Circuit,  Closed 9 

Circuits,  Divided 16 

Cleats     93-186 

Compensator  Coils 168 

Conductors    10 

Concealed    Wiring 98-128-131-138 

Condensers    211 

Conductors    ( See   Wires) 

Conduits,  Installation  of 147 

Conduits.  Lined   Metal 182 

Conduits,  To  Be  Marked 182 

Conduits,  Unlined   Metal 183 

r-ondults.  Wire  for 180 

Conduit  Work 141 

Constant  Current  Systems 32-108 


INDEX 

Constant  Potential  Systems...  <ttii4 

Coulomb T ^il 

Converters  (See  Transformers) 

Current    710 

Currents  for  Motors 65 

Cut-Out  Cabinets 150-107-123-202 

Cut-Outs,  Construction  of , 

Cut-Outs,  Installation  of .,  105-114 

Cut-Outs,  To  Be  Double  Pole 105 

Decorative  Lighting  Systems ,  ](J8 

Distance  Between  Conductors,  Inside 111-13G-141 

Distance  Between  Conductors,  Outside 78 

Drip  Loops  at  Service  Entrance 80-116 

Dynamo   Kooms 47 

Economy  Coils lt>g 

Electric  Gas  Lighting .  215 

Electric  Heaters 129 

Electro-Magnetic  Devices  for  Switches 114 

Electro-Motive    Force 11 

Electrolysis 100 

Equalizers    50 

Extra  High  Potential  Systems 172 

Feeders,    Railway 1GO 

Fished    Wires 133-142 

Fittings  and  Materials 373 

Fixtures     158 

Fixture   Wire .179 

Fixture    Wiring 14(5 

Flexible  Cord,  Construction  of 117 

Flexible  Cord,  Construction  of.  Heaters 179 

Flexible  Cord,  Construction  of,  Pendants 178 

Flexible  Cord,  Construction  of,  Portables 178 

Flexible  Cord.  Use  of 105 

Flexible  Tubing 142 

Foreign  Currents,  Protection  Against 213 

Formula  for  Soldering  Fluid 95 

Fuses,  Construction  of 199 

Fuses,  Installation  of 114-221 

Gas  Liehting.  Electric 215 

Generators 47 

Ground    Connections 90-154 

Ground    Detectors 59-62 

Grounded  Trolley  Circuits 170 

Ground'ng  Low  Potential  Circuits 88 

Grounding  of  Dynamo  and  Motor  Frames 47-63 

Grounds.   Testing   for 59 

Ground  Wire  for  Lightning  Arresters 57-213 

Hanger  Boards,  Construction  of 208 

Haneer  Boards.  When  Not  Used 113 

Heaters.  Electric 

High.  Constant  Potential  Systems 170 

ii 


INDEX 

Incandescent  Lamps  as  Resistances 56-168 

Incandescent  Lamps  in  Series  Circuits 114-168 

Induction   Coil 25 

Inside  Work 92 

Insulators    10 

Insulating  Joints,  Construction  of 209 

Insulating  Joints,  When  Required 158 

Insulation  of  Trolley  Wires 82 

Insulation  Resistance 61-216 

Interior  Conduits   (See  Conduit) 

Joints  in  Conductors 80-93 

Joints,  Insulating  (See  Insulating  Joints) 

Knob  and  Tube  Work 03 

>nmps,  Arc   (See  Arc  Lamps) 

.;i nips.    Incandescent   Series 114-168 

,ightnlng  Arresters,  Construction  of 212 

>ightning  Arresters,  Installation  of ' 57 

ights  from  Trolley  Circuits 170 

oop    System 143 

Low  Potential   Systems 131 

Mechanical  Injury,  Protection  Against 111-133-171 

Motors   63 

Moulding,  Construction  of 185 

Moulding    Work 138 

Moving   Picture  Machines 216 

Multiple  Series   System 34-74 

Ohms   Law 13 

Ohm    12 

Oily  Waste 59 

Open  Wiring 135 

Outlet  Boxes 149-184 

Outside  Work 78-83-86-88 

Panel   Boards 201 

Picture    (Moving)    Machines 216 

Pole    Lines 81 

Portable  Conductors 178 

Power 14 

Power  from  Trolley   Circuits 170 

Practical    Hints 217 

Protective  Devices,  Signal  Circuits 213 

Railway  Power  Plants ,  76 

Reactive    Coils 211 

Reinforcing    Wires 120 

Resistance    12-41 

Resistance  Boxes,  Construction  of 210 

resistance  Boxes,  Installation  of 55 

"'•sistar-ce  for  Arc  Lamp,  Low  Potential 168 

Rheostats  (See  Resistance  Boxes) 

in 


INDEX 


Sag  in  Outside  Wires 79 

Series  Arc  System :....,  32 

Series  Lamps IRQ  171 

Series  Multiple   System ."  35.74 

Service  Blocks  and  Wires 78 

Service   Switches 124 

Signaling  Systems    213 

Sockets,   Construction  of 205 

Sockets,   Installation   of 163 

Soldering  Fluid  Formula 95 

Spark  Arresters,  Construction  of 209 

Spark  Arresters,  When  Required 113-168 

Square   Mil 40 

Starting   Boxes 67-71 

Stations,  Central 47 

Static  Electricity,  Overcoming 50 

Storage  Battery   Rooms 76 

Switch  Boards 53 

Switches    Construction  of 188 

Switches     Electro-Magnetic 114 

Switches    Installation  of 105-124 

Switches    To  Be  Double  Pole 105 

Switches    When  May  Be  Single  Pole 65-126 

Systems,  Constant  Current 108 

Systems.  Constant  Potential 

Systems,  Extra  High,  Constant  Potential 172 

Systems,  High,  Constant  Potential 170 

Systems,  Low,  Constant  Potential 114 

Tables 229  to  243 

Tablet    Boards 201 

Telegraph,  Telephone  and  Other  Signal  Circuits.  .  .  .  213 

Telephones    23 

Testing    59-162-217 

Three    Wire   System 33-117-121-131-218 

Transformers  in  Central   Stations 77 

Transformers,  Construction  of 212 

Transformers,    Inside 171 

Transformers,    Outside 86 

Transmission,   Electric 36 

Transmission  Lines,  Over  5,000  Volts 83 

Tricks    of    Trade 224 

Trolley  Circuits,  Grounded 170 

Tubes,  Insulating 97-185 

Volt    11 

Watt    15 

Wire,  Concentric 

Wire.    Conduit 

Wire,    Fixture 17,9 

Wire,  Insulation  of J^g 

Wire,  Netting  Required  on  Arc  Lamps lld-lOe 

Wire,  Rubber  Covered 173 

IV 


INDEX 

Wire,  Slow  Burning 176 

Wire,  Slow  Burning,  Weather  1'roof 1  T:. 

Wire,   Weather   Proof 177 

Wires,  Car  Work 169 

Wires,  Carrying  Capacity,  Table 226 

Wiring    Tables 227 

Wires,  Central   Stations 52 

Wires,  Concealed  Knob  and  Tube  Work 141 

Wires,  Conduit  Work 141 

Wires,  Number  in  Conduit 222 

Wires,  Distance  Between   Inside 111-136-137-141 

Wires.  Distance  Between  Outside 78 

Wires,  Dynamo  Rooms 52 

Wires,    Extra   High   Potential 17D 

Wires,    Fished 133-142 

Wires,    Fixture    Work 146 

Wires,  Low  Potential.  General  Rules 131 

Wires,  Ground  Return 83 

Wires,   High  Potential • 170 

Wires,    Inside,   Constant  Current 108 

Wires,  Inside,  General  Rules !>2 

Wires.    Underground 104 

Wires.    Moulding    Work IBS 

Wires,  Open  Work,  Damp  Places 137-104 

Wires,  Open  Work.  Dry  Places 135 

Wires,   Outside,   Overhead 78-S3 

Wires,    Service 78 

Wires.   Signal 21  3 

Wires,   Trolley 82 

Wiring  Systems 117 


THE  MOST  IMPORTANT  BOOK  ON  ELECTRICAL  CONSTRUCTION 

WORK    FOR    ELECTRICAL    WORKERS    EVER  PUBLISHED 

NEW  1904    EDITION. 

MODERN    WIRING 
DIAGRAMS  AND  DESCRIPTIONS 

A  Hand  Book  of  practical  diagrams  and 
information  for  Electrical  Workers. 

Sy  HENRY  C.  HORSTMANN  and 
VICTOR  II.  TOUSLEY 
Expert  Electricians. 

This  grand  little  volume  noc  -only  tells 
you  how  to  do  it,  but  it  shows  you. 

The  book  contains  no  pictures  of 
bells,  batteries  or  other  fittings ;  you  can 
see  those  anywhere. 

It  contains  no  Fire  Underwriters' 
rules;  you  can  get  those  free  anywhere. 
It  contains  no  elementary  considera- 
tions; you  are  supposed  to  know  what 
an  ampere,  a  volt  or  a  "short  circuit" 
is.  And  it  contains  no  historical  matter. 
All  of  these  have  been  omitted  to 
make  room  for  "diagrams  and  de- 
scriptions" of  just  such  a  character  as 
workers  need.  We  claim  to  give  all 
that  ordinary  electrical  workers  neec1 
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It  shows  you  how  to  wire  for  call  and  alarm  bells. 

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How  to  run  bells  from  dynamo  current, 

How  to  install  and  manage  batteries. 

How  to  test  batteries. 

How  to  test  circuits. 

How  to  wire  for  annunciators;  for  telegraph  and  gas  lighting. 

It  tells  how  to  locate  "trouble"  and  "ring  out"  circuits. 

It  tells  about  meters  and  transformers. 

It  contains  30  diagrams  of  electric  lighting  circuits  alone. 

It  explains  dynamos  and  motors;  alternating  and  direct  current. 

It  gives  ten  diagrams  of  ground  detectors  alone. 

It  gives   "Compensator"  and  storage  battery  installation. 

It  gives  simple  and  explicit  explanation  of  the  "Wheatstoue"  Bridge 
and  its  uses  as  well  as  volt-meter  and  other  testing. 

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losses  or  distances. 

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Sold  by  booksellers  generally  or  sent  postpaid  to  any  address 
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FREDERICK  J.  DRAKE  &  COMPANY 

PUBLISHERS 
aii-213  East  Madison  Street          CHICAGO,  U.S.A. 


DYNAMO  TENDING 

for 

ENGINEERS 


Or,  ELECTRICITY 
FOR  STEAM  ENGINEERS 

By  HENRY  C.  HORSTMANN  and 

VICTOR  H.  TOUSLEY, 
Authors  of  "Modern  Wiring  Diagrams  and 
Descriptions  for  Electrical  Workers." 


This  excellent  treatise  is  written  by 
engineers  for  engineers,  and  is  a  clear 
and  comprehensive  treatise  on  the  prin- 
ciples, construction  and  operation  of 
Dynamos,  Motors,  Lamps,  Storage  Bat- 
teries, Indicators  and  Measuring  Instru- 
ments, as  well  as  full  explanations  of  the 
principles  governing  the  generation 
of  alternating  currents  and  a  descrip- 
tion of  alternating  current  Instruments  and  machinery.  There  are 
perhaps  but  few  engineers  who  have  not  in  the  course  of  their  labors 
come  in  contact  with  the  electrical  apparatus  such  as  pertains  to  light 
and  power  distribution  and  generation.  At  the  present  rate  of  increase 
in  the  use  of  Electricity  it  is  but  a  question  of  time  when  every  steam 
installation  will  have  in  connecton  with  it  an  electrical  generator,  even 
in  such  buildings  where  light  and  power  are  supplied  by  some  central 
station.  It  is  essential  that  the  man  in  charge  of  Engines,  Boilers. 
Elevators,  etc.,  be  familiar  with  electrical  matters,  and  it  cannot  well 
be  other  than  an  advantage  to  him  and  his  employers.  It  Is  with  a  view 
to  assisting  engineers  and  others  to  obtain  such  knowledge  as  will  enable 
them  to  intelligently  manage  such  electrical  apparatus  as  will  ordinarily 
•come  under  their  control  that  this  book  has  been  written.  The  authors 
have  had  the  co-operation  of  the  best  authorities,  each  in  his  chosen  field, 
and  the  information  given  is  just  such  as  a  steam  engineer  should  know, 
To  further  this  information,  and  to  more  carefully  explain  the  text, 
nearly  100  illustrations  are  used,  which,  with  perhaps  a  very  few  excep- 
tions, have  been  especially  made  for  this  book.  There  are  many  tables 
covering  all  sorts  of  electrical  matters,  so  that  immediate  reference  can 
be  made  without  resorting  to  figuring.  It  covers  the  subject  thoroughly, 
but  so  simply  that  any  one  can  understand  it  fully.  Any  one  making  a 
pretense  to  electrical  engineering  needs  this  book.  Nothing  keeps  a  man 
down  like  the  lack  of  training;  nothing  lifts  him  up  as  quickly  or  as 
surely  as  a  thorough,  practical  knowledge  of  the  work  he  has  to  do.  This 
book  was  written  for  the  man  without  an  opportunity.  No  matter  what 
he  is,  or  what  work  he  has  to  do,  it  gives  mm  just  such  information 
and  training  as  are  required  to  attain  success.  It  teaches  just  what 
the  steam  engineer  should  know  in  his  engine  room  about  electricity, 
r.'ini)  Cloth,  1OO  Illustrations.  <i/..  r,  \:  .  PRICE  NET  Al  r  A 
Sold  by  booksellers  generally,  or  sent,  all  charges  paid,  upon  $liwU 
receipt  of  price  ' 

FREDERICK  J.  DRAKE  £  COMPANY 

Publishers  of  Self -Educational  Books  for  Mechanics 

2II-3I3  East  Madison  Street  CHICAGO.  U.S.A. 


Easy  Electrical  Experiment* 
and  How  tf>  Make  Them 

By  L.  P.  DICKINSON 

This  is  the  very  latest  and  most 
valuable  work  on  Electricity  for  the 
amateur  or  practical  Electrician  pub- 
lished. It  gives  in  a  simple  and 
easily  understood  language  every 
thing  you  should  know  about  Gal- 
vanometers, Batteries,  Magnets,  In- 
duction, Coils,  Motors,  Voltmeters, 
Dynamos,  Storage  Batteries,  Simple 
and  Practical  Telephones,  Telegraph 
Instruments,  Rheostat,  Condensers,  Electrophorous, 
Resistance,  Electro  Plating,  Electric  Toy  Making,  etc. 
The  book  is  an  elementary  hand  book  of  lessons, 
experiments  and  inventions.  It  is  a  hand  book  for 
beginners,  though  it  includes,  as  well,  examples  for 
the  advanced  students.  The  author  stands  second  to 
none  in  the  scientific  world,  and  this  exhaustive  work 
will  be  found  an  invaluable  assistant  to  either  the 
student  or  mechanic. 

Illustrated  with  hundreds  of  fine  drawings;  printed 
on  a  superior  quality  of  paper. 

J2mo  Cloth.       Price,  $J.25. 

Sent  postpaid  to  any  address  upon  receipt  of  price. 

FR.EDER.ICK   J.   DRAKE  <&   CO. 

PUBLISHERS    •  

3  J  3  *  Chicago 


A  BOOK  EVERY  ENGINEER  AND  ELECTRICIAN 
SHOULD  HAVE  IN  HIS  POCKET.  A  COMPLETE 
ELECTRICAL  REFERENCE  LIBRARY  IN  ITSELF 

NEW    EDITION 
Handy  Vest-Pocket 

ELECTRICAL 
DICTIONARY 

BY  WM.  L.  WEBER,  M.E. 
ILLUSTRATED 

/CONTAINS  upwards  of  4,800  words, 
t;  terms  and  phrases  employed  in  the 
electrical  profession,  with  their 
definitions  given  in  the  most  concise, 
lucid  and  comprehensive  manner. 

The  practical  business  advantage 
and  the  educational  benefit  derived 
from  the  ability  to  at  ouce  understand 
the  meaning  of  some  term  involving 
the  description,  action  or  functions  of 
a  machine  or  apparatus,  or  the  physi- 
cal nature  and  cause  of  certain  phe- 
nomena, cannot  be  overestimated,  and 
will  not  be,  by  the  thoughtful  assidu- 
ous and  ambitious  electrician,  because 
he  knows  that  a  thorough  understand- 
ing, on  the  spot,  and  in  the  presence 
of  any  phenomena,  effected  by  the  aid 
of  his  little  vest-pocket  book  of  refer- 
ence, is  far  more  valuable  and  lasting 
in  its  impression  upon  the  mind,  than 
any  memorandum  which  he  might 
make  a*  the  time,  with  a  view  to  the 
future  consultation  of  some  volumin- 
ous standard  textbook,  and  which  is 
more  frequently  neglected  or  forgotten 
than  done. 

The  book  is  of  convenient  size  for 
carrying  in  the  vest  pocket,  being  only 
2%  inches  by  5Yt  inches,  and  K  inch 
thick;  224  pages,  illustrated,  and 
bound  in  two  different  styles: 

New  Edition.  Cloth,  Red  Edges,  Indexed  .  .  25c 
New  Edition.  Full  Leather,  Gold  Edges,  Indexed,  50c 

Sold  by  booksellers  generally  or  sent  postpaid  to  any  address  upon  receipt 

FREDERICK  J.  1)RAKE  &   COMPANY 

Publishers  of  Self-Educational  Books  for  Mechanics 
311-213  E.  MADISON  ST.  •  CHICAGO,  U.S.A 


BOOKKEEPING 
SELF-TAUGHT 


By  PHILLIP  C.  GOODWIN : 


FEW,  if  any  of  of  the  technical  works  J 
which  purport  to  be  self-instructing? 
have  justified  the  claims  made  for* 
them,    and  invariably  the  student 
either  becomes  discouraged  and  abandons 
his  purpose  and  aim,  or  he  is  compelled  to 
enlist  the  offices  of  a  professional  teacher,* 
which  in  the  great  majority  of  instances  is' 
impracticable  when  considered  in  relation 
to  the  demands  upon  time  and  the  condi- 
tion of  life  to  which  the  great  busy  public  i» 
subjected. 

Mr.  Goodwin's  treatise  on  Bookkeeping 
is  an  entirely  new  departure  from  all 
former  methods  of  self-instruction  and  one 
which  can  be  studied  systematically  and 
alone  by  the  student  with  quick  and 
permanent  results,  or  taken  up  in  leisure 
moments  with  an  absolute  certainty  of  ac- 
quiring t  he-science  in  a  very  short  time  and 
with  little  effort.  The  book  is  both  a 
marvel  of  skill  and  simplicity.  Every 
featuif  and  every  detail  leading  to  the 
"  p.axof  scientific  perfection  are  so  thor- 


oughly  complete  in  this  logical  procedure 
thorough    anvl  delily  made  that   the  self-teaching 


and  the  analysis  so  thorough    anu  deUly  ro 

student  is  led  by  almost  imperceptible,  but  sure  and  certain  steps  to 
the  basic  principles  of  the  science,  whicn  the  author  in  a  most  compre- 
yle 


Tne  wprK  is  tne  most  masterly  ex 
Bookkeeping  and  their  practical  appli 
English  language,  and  it  should  be  ia 
every  clerk,  farmer,  teacher  and  I 


hensive  and  lucid  style  lays  bare  to  intelligence  of,  even  the  most 
mediocre  order. 

The  work  is  the  most  masterly  exposition  of  the  scientific  principles  of 
jlication  which  has  ever  appeared  in  the 
i  the  hands  of  every  school  boy  or  girl, 
business  or  professional  man;  fora 

knowledge  Of  Bookkeeping,  even  though  it  may  not  be  followed  as  a  pro- 
fession, is  a  necessity  felt  by  every  person  in  business  life  and  a  recognized 
prime  factor  of  business  success.  , 

In  addition  to  a  very  simple  yet  elaborate  explanation  in  detail  of  tne 
eystems  of  both  single  and  double  entry  Bookkeeping,  beginning  with  the 
initial  transactions  and  leading  the  student  along  to  the  culminating  exhibit 
of  the  balance  sheet,  the  work  contains  a  glossary  of  all  the  commercial 
terms  employed  in  the  business  world,  together  with  accounts  in  illustra-j 
ton,  exercises  for  practice  and  one  set  of  books  completely  written  up, 

I2mo  Cloth.    Price  $1.00. 
Sent  postpaid  to  any  address  upon  receipt  of  price. 

Frederick  J.  Drake  &  Co.,   Publishers 

2  1  2(3  EAST  MADISON  ST.,  CHICAGO 


NOTICE 


To  the  many  workmen  who  are  purchasing  the  publications  under  the 
authorship  of  Fred  T.  Hodgson,  and  who  we  feel  sure  have  been  benefited 
by  his  excellent  treatises  on  many  Carpentry  and  Building  subjects,  we 
desire  to  inform  them  that  the  following  list  of  books  have  been  published 
since  1903,  thereby  making  them  strictly  up-to-date  in  every  detail.  All  of 
the  newer  books  bearing  the  imprint  of  Frederick  J.  Drake  &  Co.  are  modern 
in  every  respect  and  of  a  purely  self-educational  character,  expressly  issued 
for  Home  Study. 

PRACTICAL  USES  OF  THE  STEEL  SQUARE,  two  volumes,  over  500 
pages,  including  100  perspective  views  and  floor  plans  of  medium- 
priced  houses.  Cloth,  two  volumes,  price  $2.00.  Half  leather, 
price  $3.00. 

MODERN  CARPENTRY  AND  JOINERY,  300  pages,  including  50  house 
plans,  perspective  views  and  floor  plans  of  medium  and  low-cost 
houses.  Cloth,  price  $1.00.  Half  leather,  price  $1.50. 

BUILDERS'  ARCHITECTURAL  DRAWING  SELF-TAUGHT,  over  350 
pages,  including  50  house  plans.  Cloth,  price  $2.00.  Half  leather, 
price  $3.00. 

MODERN  ESTIMATOR  AND  CONTRACTORS'  GUIDE,  for  pricing  build- 
ers' work,  350  pages,  including  50  house  plans.  Cloth,  price  $1.50. 
Half  leather,  price  $2.00. 

MODERN  LOW-COST  AMERICAN  HOMES,  over  200  pages.  Cloth,  pria 
$1.00.  Half  leather,  price  $1.50. 

PRACTICAL  UP-TO-DATE  HARDWOOD  FINISHER,  over  300  pages. 
Cloth,  price  $1.00.  Half  Leather,  price  $1.50. 

COMMON  SENSE  STAIR  BUILDING  AND  HANDRAILING,  over  250 
pages,  including  perspective  views  and  floor  plans  of  50  medium-priced 
houses.  Cloth,  price  $1.00.  Half  leather,  price  $1.50. 

STONEMASONS'  AND  BRICKLAYERS'  GUIDE,  over  200  pages.  Cloth, 
price  91. 50.  Half  leather,  price  $2 . 00. 

PRACTICAL  WOOD  CARVING,  over  200  pages.  Cloth,  price  $1.50.  Half 
leather,  price  $2.00. 

Sold  by  booksellers  generally,  or  sent,  all  charges  paid,  upon  receipt  of 
price,  to  any  address  in  the  world. 

FREDERICK  J.  DRAKE  &   CO. 

Publishers 
211-213  E.  Madison  St.,  Chicago,  U.  S.  A. 


UNIVERSITY  OF  CALIFORNIA  AT  LOS  ANGELES 
THE  UNIVERSITY  LIBRARY 


This  book  is  DUE  on  the  last  date  stamped  below* 


r 


H   9901     Horstmann  - 
H78m Modern  elec 


